CUB-128: Build Settings page

frontend/src/App.tsx

@@ -1,51 +1,53 @@
 import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
 import { BrowserRouter, Routes, Route, NavLink } from 'react-router-dom'
-import { Box, Printer } from 'lucide-react'
+import { Package, Settings } from 'lucide-react'
 import InventoryPage from './pages/InventoryPage'
-import PrintersPage from './pages/PrintersPage'
+import SettingsPage from './pages/SettingsPage'
 
 const queryClient = new QueryClient()
 
-function NavItem({ to, icon: Icon, label }: { to: string; icon: React.ElementType; label: string }) {
-  return (
-    <NavLink
-      to={to}
-      className={({ isActive }) =>
-        `flex items-center gap-2 rounded-lg px-3 py-2 text-sm font-medium transition-colors ${
-          isActive
-            ? 'bg-emerald-600/20 text-emerald-300'
-            : 'text-slate-300 hover:bg-slate-700/50 hover:text-slate-100'
-        }`
-      }
-    >
-      <Icon size={16} />
-      <span>{label}</span>
-    </NavLink>
-  )
-}
-
 export default function App() {
   return (
     <QueryClientProvider client={queryClient}>
       <BrowserRouter>
         <div className="min-h-screen bg-slate-900 text-slate-50">
-          <header className="bg-slate-800 border-b border-slate-700 px-4 py-3 flex items-center gap-3 sticky top-0 z-20">
-            <div className="w-8 h-8 rounded bg-emerald-500 flex items-center justify-center text-slate-900 font-bold text-lg">E</div>
-            <h1 className="text-lg font-semibold">Extrudex</h1>
-            <nav className="ml-4 hidden sm:flex items-center gap-1">
-              <NavItem to="/" icon={Box} label="Inventory" />
-              <NavItem to="/printers" icon={Printer} label="Printers" />
+          <header className="bg-slate-800 border-b border-slate-700 px-4 py-3 flex items-center gap-4 sticky top-0 z-20">
+            <div className="flex items-center gap-3 mr-4">
+              <div className="w-8 h-8 rounded bg-emerald-500 flex items-center justify-center text-slate-900 font-bold text-lg">E</div>
+              <h1 className="text-lg font-semibold">Extrudex</h1>
+            </div>
+            <nav className="flex items-center gap-1">
+              <NavLink
+                to="/"
+                end
+                className={({ isActive }) =>
+                  `inline-flex items-center gap-1.5 rounded-md px-3 py-1.5 text-sm font-medium transition-colors ${
+                    isActive
+                      ? 'bg-emerald-600/20 text-emerald-400'
+                      : 'text-slate-400 hover:text-slate-200 hover:bg-slate-700'
+                  }`
+                }
+              >
+                <Package size={15} /> Inventory
+              </NavLink>
+              <NavLink
+                to="/settings"
+                className={({ isActive }) =>
+                  `inline-flex items-center gap-1.5 rounded-md px-3 py-1.5 text-sm font-medium transition-colors ${
+                    isActive
+                      ? 'bg-emerald-600/20 text-emerald-400'
+                      : 'text-slate-400 hover:text-slate-200 hover:bg-slate-700'
+                  }`
+                }
+              >
+                <Settings size={15} /> Settings
+              </NavLink>
             </nav>
           </header>
-          {/* Mobile nav */}
-          <nav className="sm:hidden bg-slate-800 border-b border-slate-700 px-4 py-2 flex items-center gap-1">
-            <NavItem to="/" icon={Box} label="Inventory" />
-            <NavItem to="/printers" icon={Printer} label="Printers" />
-          </nav>
           <main className="p-4">
             <Routes>
               <Route path="/" element={<InventoryPage />} />
-              <Route path="/printers" element={<PrintersPage />} />
+              <Route path="/settings" element={<SettingsPage />} />
             </Routes>
           </main>
         </div>

frontend/src/pages/PrintersPage.tsx

@@ -1,468 +0,0 @@
-import { useState, useMemo } from 'react'
-import { useQuery } from '@tanstack/react-query'
-import {
-  Search,
-  Wifi,
-  WifiOff,
-  HelpCircle,
-  Pencil,
-  Plus,
-  Trash2,
-  AlertTriangle,
-  ChevronLeft,
-  ChevronRight,
-  Server,
-  Radio,
-  ShieldCheck,
-} from 'lucide-react'
-import { fetchPrinters } from '../services/printerService'
-import type { Printer } from '../types/printer'
-
-const PAGE_SIZE = 20
-
-type SortField = 'name' | 'printer_type' | 'manufacturer' | 'model'
-type SortDir = 'asc' | 'desc'
-
-type ConnStatus = 'online' | 'offline' | 'unknown'
-
-export default function PrintersPage() {
-  const [search, setSearch] = useState('')
-  const [statusFilter, setStatusFilter] = useState<ConnStatus | ''>('')
-  const [typeFilter, setTypeFilter] = useState('')
-  const [sortBy, setSortBy] = useState<SortField>('name')
-  const [sortDir, setSortDir] = useState<SortDir>('asc')
-  const [page, setPage] = useState(0)
-  const [deleteId, setDeleteId] = useState<number | null>(null)
-
-  const {
-    data: printers,
-    isLoading,
-    error,
-    refetch,
-  } = useQuery({
-    queryKey: ['printers'],
-    queryFn: fetchPrinters,
-  })
-
-  // Derive connection status from backend is_active for now
-  // TODO: replace with real status endpoint / SSE when available
-  const printersWithStatus = useMemo(() => {
-    return (printers ?? []).map((p) => {
-      const status: ConnStatus = p.is_active ? 'online' : 'offline'
-      return { ...p, connection_status: status }
-    })
-  }, [printers])
-
-  // Client-side filter + sort
-  const filtered = useMemo(() => {
-    let list = [...printersWithStatus]
-
-    if (search.trim()) {
-      const q = search.toLowerCase()
-      list = list.filter(
-        (p) =>
-          p.name.toLowerCase().includes(q) ||
-          (p.manufacturer?.toLowerCase().includes(q) ?? false) ||
-          (p.model?.toLowerCase().includes(q) ?? false)
-      )
-    }
-
-    if (statusFilter) {
-      list = list.filter((p) => p.connection_status === statusFilter)
-    }
-
-    if (typeFilter) {
-      list = list.filter((p) => p.printer_type?.name === typeFilter)
-    }
-
-    list.sort((a, b) => {
-      const dir = sortDir === 'asc' ? 1 : -1
-      switch (sortBy) {
-        case 'name':
-          return a.name.localeCompare(b.name) * dir
-        case 'printer_type':
-          return (a.printer_type?.name ?? '').localeCompare(b.printer_type?.name ?? '') * dir
-        case 'manufacturer':
-          return (a.manufacturer ?? '').localeCompare(b.manufacturer ?? '') * dir
-        case 'model':
-          return (a.model ?? '').localeCompare(b.model ?? '') * dir
-        default:
-          return 0
-      }
-    })
-
-    return list
-  }, [printersWithStatus, search, statusFilter, typeFilter, sortBy, sortDir])
-
-  const total = filtered.length
-  const totalPages = Math.max(1, Math.ceil(total / PAGE_SIZE))
-  const pageItems = filtered.slice(page * PAGE_SIZE, (page + 1) * PAGE_SIZE)
-
-  const uniqueTypes = useMemo(() => {
-    const s = new Set<string>()
-    ;(printers ?? []).forEach((p) => {
-      if (p.printer_type?.name) s.add(p.printer_type.name)
-    })
-    return Array.from(s).sort()
-  }, [printers])
-
-  const handleSort = (field: SortField) => {
-    if (sortBy === field) {
-      setSortDir((prev) => (prev === 'asc' ? 'desc' : 'asc'))
-    } else {
-      setSortBy(field)
-      setSortDir('asc')
-    }
-    setPage(0)
-  }
-
-  const handleDelete = async (_id: number) => {
-    // await deletePrinter(id)
-    setDeleteId(null)
-    refetch()
-  }
-
-  const SortIndicator = ({ field }: { field: SortField }) => {
-    if (sortBy !== field) return <span className="text-slate-600 ml-1">↕</span>
-    return <span className="text-emerald-400 ml-1">{sortDir === 'asc' ? '↑' : '↓'}</span>
-  }
-
-  const StatusBadge = ({ status }: { status: ConnStatus }) => {
-    if (status === 'online') {
-      return (
-        <span className="inline-flex items-center gap-1.5 rounded-full bg-emerald-900/30 border border-emerald-700 px-2.5 py-1 text-xs font-medium text-emerald-300">
-          <Wifi size={12} /> Online
-        </span>
-      )
-    }
-    if (status === 'offline') {
-      return (
-        <span className="inline-flex items-center gap-1.5 rounded-full bg-red-900/30 border border-red-700 px-2.5 py-1 text-xs font-medium text-red-300">
-          <WifiOff size={12} /> Offline
-        </span>
-      )
-    }
-    return (
-      <span className="inline-flex items-center gap-1.5 rounded-full bg-slate-700/50 border border-slate-600 px-2.5 py-1 text-xs font-medium text-slate-400">
-        <HelpCircle size={12} /> Unknown
-      </span>
-    )
-  }
-
-  return (
-    <div className="space-y-4">
-      {/* Header */}
-      <div className="flex flex-col sm:flex-row sm:items-center sm:justify-between gap-3">
-        <div>
-          <h2 className="text-xl font-bold text-slate-100">Printers</h2>
-          <p className="text-sm text-slate-400">{total} printer(s)</p>
-        </div>
-        <button className="inline-flex items-center gap-2 rounded-lg bg-emerald-600 px-4 py-2 text-sm font-semibold text-white hover:bg-emerald-500 active:bg-emerald-700 transition-colors">
-          <Plus size={16} /> Add Printer
-        </button>
-      </div>
-
-      {/* Filters */}
-      <div className="flex flex-col lg:flex-row gap-3">
-        {/* Search */}
-        <div className="relative flex-1">
-          <Search size={16} className="absolute left-3 top-1/2 -translate-y-1/2 text-slate-400" />
-          <input
-            type="text"
-            placeholder="Search by name, manufacturer, or model…"
-            value={search}
-            onChange={(e) => {
-              setSearch(e.target.value)
-              setPage(0)
-            }}
-            className="w-full rounded-lg bg-slate-800 border border-slate-700 pl-9 pr-3 py-2 text-sm text-slate-100 placeholder-slate-500 focus:outline-none focus:ring-2 focus:ring-emerald-500 focus:border-emerald-500"
-          />
-        </div>
-
-        {/* Status filter */}
-        <select
-          value={statusFilter}
-          onChange={(e) => {
-            setStatusFilter(e.target.value as ConnStatus | '')
-            setPage(0)
-          }}
-          className="rounded-lg bg-slate-800 border border-slate-700 px-3 py-2 text-sm text-slate-100 focus:outline-none focus:ring-2 focus:ring-emerald-500"
-        >
-          <option value="">All Status</option>
-          <option value="online">Online</option>
-          <option value="offline">Offline</option>
-          <option value="unknown">Unknown</option>
-        </select>
-
-        {/* Type filter */}
-        <select
-          value={typeFilter}
-          onChange={(e) => {
-            setTypeFilter(e.target.value)
-            setPage(0)
-          }}
-          className="rounded-lg bg-slate-800 border border-slate-700 px-3 py-2 text-sm text-slate-100 focus:outline-none focus:ring-2 focus:ring-emerald-500"
-        >
-          <option value="">All Types</option>
-          {uniqueTypes.map((t) => (
-            <option key={t} value={t}>
-              {t}
-            </option>
-          ))}
-        </select>
-      </div>
-
-      {/* Loading / Error */}
-      {isLoading && <div className="text-center py-12 text-slate-400">Loading printers…</div>}
-      {error && (
-        <div className="text-center py-12 text-red-400">
-          Failed to load printers.
-          <button onClick={() => refetch()} className="ml-2 underline hover:text-red-300">
-            Retry
-          </button>
-        </div>
-      )}
-
-      {/* Desktop Table */}
-      {!isLoading && !error && (
-        <>
-          <div className="hidden md:block overflow-x-auto rounded-lg border border-slate-700">
-            <table className="w-full text-sm">
-              <thead className="bg-slate-800 text-slate-300">
-                <tr>
-                  <th
-                    className="px-4 py-3 text-left font-semibold cursor-pointer select-none hover:text-slate-100"
-                    onClick={() => handleSort('name')}
-                  >
-                    Name <SortIndicator field="name" />
-                  </th>
-                  <th
-                    className="px-4 py-3 text-left font-semibold cursor-pointer select-none hover:text-slate-100"
-                    onClick={() => handleSort('printer_type')}
-                  >
-                    Type <SortIndicator field="printer_type" />
-                  </th>
-                  <th
-                    className="px-4 py-3 text-left font-semibold cursor-pointer select-none hover:text-slate-100"
-                    onClick={() => handleSort('manufacturer')}
-                  >
-                    Manufacturer <SortIndicator field="manufacturer" />
-                  </th>
-                  <th
-                    className="px-4 py-3 text-left font-semibold cursor-pointer select-none hover:text-slate-100"
-                    onClick={() => handleSort('model')}
-                  >
-                    Model <SortIndicator field="model" />
-                  </th>
-                  <th className="px-4 py-3 text-left font-semibold">Connection</th>
-                  <th className="px-4 py-3 text-left font-semibold">Moonraker</th>
-                  <th className="px-4 py-3 text-left font-semibold">MQTT</th>
-                  <th className="px-4 py-3 text-right font-semibold">Actions</th>
-                </tr>
-              </thead>
-              <tbody className="divide-y divide-slate-700">
-                {pageItems.length === 0 && (
-                  <tr>
-                    <td colSpan={8} className="px-4 py-8 text-center text-slate-500">
-                      No printers found.
-                    </td>
-                  </tr>
-                )}
-                {pageItems.map((p: Printer & { connection_status: ConnStatus }) => (
-                  <tr key={p.id} className="bg-slate-800/50 hover:bg-slate-700/50 transition-colors">
-                    <td className="px-4 py-3 font-medium text-slate-100">{p.name}</td>
-                    <td className="px-4 py-3 text-slate-300">
-                      <span className="inline-flex items-center gap-1.5 rounded-md bg-slate-700/50 px-2 py-0.5 text-xs">
-                        {p.printer_type?.name ?? '—'}
-                      </span>
-                    </td>
-                    <td className="px-4 py-3 text-slate-300">{p.manufacturer ?? '—'}</td>
-                    <td className="px-4 py-3 text-slate-300">{p.model ?? '—'}</td>
-                    <td className="px-4 py-3">
-                      <StatusBadge status={p.connection_status} />
-                    </td>
-                    <td className="px-4 py-3 text-slate-300">
-                      {p.moonraker_url ? (
-                        <span className="inline-flex items-center gap-1.5 text-xs text-blue-300">
-                          <Server size={12} />
-                          <a
-                            href={p.moonraker_url}
-                            target="_blank"
-                            rel="noopener noreferrer"
-                            className="hover:underline truncate max-w-[160px] inline-block"
-                            title={p.moonraker_url}
-                          >
-                            {p.moonraker_url}
-                          </a>
-                        </span>
-                      ) : (
-                        <span className="text-slate-500 text-xs">—</span>
-                      )}
-                    </td>
-                    <td className="px-4 py-3">
-                      {p.mqtt_broker_host ? (
-                        <span className="inline-flex items-center gap-1 text-xs text-slate-300">
-                          <Radio size={12} className="text-emerald-400" />
-                          {p.mqtt_topic_prefix ? `${p.mqtt_topic_prefix} @ ` : ''}
-                          {p.mqtt_broker_host}
-                          {p.mqtt_tls_enabled && (
-                            <span title="TLS enabled">
-                              <ShieldCheck size={12} className="text-emerald-400" />
-                            </span>
-                          )}
-                        </span>
-                      ) : (
-                        <span className="text-slate-500 text-xs">—</span>
-                      )}
-                    </td>
-                    <td className="px-4 py-3 text-right">
-                      <div className="flex items-center justify-end gap-2">
-                        <button
-                          className="p-1.5 rounded hover:bg-slate-600 text-slate-400 hover:text-blue-400 transition-colors"
-                          title="Edit"
-                        >
-                          <Pencil size={14} />
-                        </button>
-                        <button
-                          onClick={() => setDeleteId(p.id)}
-                          className="p-1.5 rounded hover:bg-slate-600 text-slate-400 hover:text-red-400 transition-colors"
-                          title="Delete"
-                        >
-                          <Trash2 size={14} />
-                        </button>
-                      </div>
-                    </td>
-                  </tr>
-                ))}
-              </tbody>
-            </table>
-          </div>
-
-          {/* Mobile Cards */}
-          <div className="md:hidden space-y-3">
-            {pageItems.length === 0 && (
-              <div className="text-center py-12 text-slate-500">No printers found.</div>
-            )}
-            {pageItems.map((p: Printer & { connection_status: ConnStatus }) => (
-              <div
-                key={p.id}
-                className="rounded-lg border border-slate-700 bg-slate-800 p-4 space-y-3"
-              >
-                <div className="flex items-start justify-between">
-                  <div>
-                    <div className="font-semibold text-slate-100">{p.name}</div>
-                    <div className="text-xs text-slate-400 mt-0.5">
-                      {p.printer_type?.name ?? '—'} · {p.manufacturer ?? '—'} {p.model ?? ''}
-                    </div>
-                  </div>
-                  <StatusBadge status={p.connection_status} />
-                </div>
-
-                {/* Moonraker */}
-                {p.moonraker_url && (
-                  <div className="flex items-center gap-2 text-sm text-slate-300">
-                    <Server size={14} className="text-blue-400 shrink-0" />
-                    <a
-                      href={p.moonraker_url}
-                      target="_blank"
-                      rel="noopener noreferrer"
-                      className="text-blue-300 hover:underline truncate"
-                    >
-                      {p.moonraker_url}
-                    </a>
-                  </div>
-                )}
-
-                {/* MQTT */}
-                {p.mqtt_broker_host && (
-                  <div className="flex items-center gap-2 text-sm text-slate-300">
-                    <Radio size={14} className="text-emerald-400 shrink-0" />
-                    <span className="truncate">
-                      {p.mqtt_topic_prefix ? `${p.mqtt_topic_prefix} @ ` : ''}
-                      {p.mqtt_broker_host}
-                      {p.mqtt_tls_enabled && (
-                        <span title="TLS enabled">
-                          <ShieldCheck size={14} className="text-emerald-400 inline ml-1" />
-                        </span>
-                      )}
-                    </span>
-                  </div>
-                )}
-
-                {/* Actions */}
-                <div className="flex items-center justify-end gap-2 pt-1">
-                  <button className="flex items-center gap-1 rounded-md bg-slate-700 px-3 py-1.5 text-xs font-medium text-slate-200 hover:bg-slate-600">
-                    <Pencil size={12} /> Edit
-                  </button>
-                  <button
-                    onClick={() => setDeleteId(p.id)}
-                    className="flex items-center gap-1 rounded-md bg-red-900/30 border border-red-700 px-3 py-1.5 text-xs font-medium text-red-300 hover:bg-red-900/50"
-                  >
-                    <Trash2 size={12} /> Delete
-                  </button>
-                </div>
-              </div>
-            ))}
-          </div>
-
-          {/* Pagination */}
-          <div className="flex items-center justify-between pt-2">
-            <span className="text-sm text-slate-400">
-              Showing {page * PAGE_SIZE + 1}–{Math.min((page + 1) * PAGE_SIZE, total)} of {total}
-            </span>
-            <div className="flex items-center gap-2">
-              <button
-                onClick={() => setPage((p) => Math.max(0, p - 1))}
-                disabled={page === 0}
-                className="p-2 rounded-lg bg-slate-800 border border-slate-700 text-slate-300 hover:bg-slate-700 disabled:opacity-40 disabled:cursor-not-allowed transition-colors"
-              >
-                <ChevronLeft size={16} />
-              </button>
-              <span className="text-sm text-slate-300 tabular-nums">
-                {page + 1} / {totalPages}
-              </span>
-              <button
-                onClick={() => setPage((p) => Math.min(totalPages - 1, p + 1))}
-                disabled={page >= totalPages - 1}
-                className="p-2 rounded-lg bg-slate-800 border border-slate-700 text-slate-300 hover:bg-slate-700 disabled:opacity-40 disabled:cursor-not-allowed transition-colors"
-              >
-                <ChevronRight size={16} />
-              </button>
-            </div>
-          </div>
-        </>
-      )}
-
-      {/* Delete confirmation modal */}
-      {deleteId !== null && (
-        <div className="fixed inset-0 z-50 flex items-center justify-center bg-black/60 backdrop-blur-sm p-4">
-          <div className="w-full max-w-sm rounded-xl bg-slate-800 border border-slate-700 p-6 shadow-2xl space-y-4">
-            <div className="flex items-center gap-3">
-              <div className="flex h-10 w-10 items-center justify-center rounded-full bg-red-900/30">
-                <AlertTriangle size={20} className="text-red-400" />
-              </div>
-              <div>
-                <h3 className="text-lg font-semibold text-slate-100">Delete Printer?</h3>
-                <p className="text-sm text-slate-400">This action cannot be undone.</p>
-              </div>
-            </div>
-            <div className="flex justify-end gap-3">
-              <button
-                onClick={() => setDeleteId(null)}
-                className="rounded-lg bg-slate-700 px-4 py-2 text-sm font-medium text-slate-200 hover:bg-slate-600 transition-colors"
-              >
-                Cancel
-              </button>
-              <button
-                onClick={() => handleDelete(deleteId)}
-                className="rounded-lg bg-red-600 px-4 py-2 text-sm font-medium text-white hover:bg-red-500 transition-colors"
-              >
-                Delete
-              </button>
-            </div>
-          </div>
-        </div>
-      )}
-    </div>
-  )
-}

frontend/src/pages/SettingsPage.tsx

@@ -0,0 +1,290 @@
+import { useState } from 'react'
+import { Save, Wifi, WifiOff, Sun, Moon, AlertCircle, CheckCircle2 } from 'lucide-react'
+
+// TODO: Replace with API calls to GET/PUT /api/settings once Dex implements the endpoint
+const DEFAULT_SETTINGS = {
+  lowStockThresholdGrams: 100,
+  filamentCrossSectionMm2: 2.405, // π × (0.875mm)² — standard 1.75mm filament
+  currency: 'USD',
+  theme: 'dark' as 'dark' | 'light' | 'system',
+}
+
+const CURRENCIES = ['USD', 'EUR', 'GBP', 'CAD', 'AUD', 'JPY']
+
+type ConnectionStatus = 'idle' | 'testing' | 'ok' | 'error'
+
+interface PrinterConfig {
+  name: string
+  type: 'bambu' | 'moonraker'
+  host: string
+}
+
+// TODO: Load from GET /api/printers once Dex implements the endpoint
+const MOCK_PRINTERS: PrinterConfig[] = [
+  { name: 'Bambu X1C #1', type: 'bambu', host: '192.168.1.100' },
+  { name: 'Bambu X1C #2', type: 'bambu', host: '192.168.1.101' },
+  { name: 'Voron 2.4 (Klipper)', type: 'moonraker', host: '192.168.1.200' },
+]
+
+function SettingRow({ label, hint, children }: { label: string; hint?: string; children: React.ReactNode }) {
+  return (
+    <div className="flex flex-col sm:flex-row sm:items-center gap-2 sm:gap-4 py-4 border-b border-slate-700 last:border-0">
+      <div className="sm:w-64 shrink-0">
+        <div className="text-sm font-medium text-slate-200">{label}</div>
+        {hint && <div className="text-xs text-slate-500 mt-0.5">{hint}</div>}
+      </div>
+      <div className="flex-1">{children}</div>
+    </div>
+  )
+}
+
+function SectionHeader({ title, description }: { title: string; description?: string }) {
+  return (
+    <div className="mb-2">
+      <h3 className="text-base font-semibold text-slate-100">{title}</h3>
+      {description && <p className="text-sm text-slate-400 mt-0.5">{description}</p>}
+    </div>
+  )
+}
+
+export default function SettingsPage() {
+  const [lowStockThreshold, setLowStockThreshold] = useState(DEFAULT_SETTINGS.lowStockThresholdGrams)
+  const [crossSection, setCrossSection] = useState(DEFAULT_SETTINGS.filamentCrossSectionMm2)
+  const [currency, setCurrency] = useState(DEFAULT_SETTINGS.currency)
+  const [theme, setTheme] = useState(DEFAULT_SETTINGS.theme)
+  const [saved, setSaved] = useState(false)
+  const [saveError, setSaveError] = useState(false)
+  const [printerStatus, setPrinterStatus] = useState<Record<string, ConnectionStatus>>({})
+
+  const [thresholdError, setThresholdError] = useState('')
+  const [crossSectionError, setCrossSectionError] = useState('')
+
+  const validate = () => {
+    let valid = true
+    if (!lowStockThreshold || lowStockThreshold < 0 || lowStockThreshold > 10000) {
+      setThresholdError('Must be between 0 and 10,000 g')
+      valid = false
+    } else {
+      setThresholdError('')
+    }
+    if (!crossSection || crossSection <= 0 || crossSection > 100) {
+      setCrossSectionError('Must be a positive number (typical: 2.405 for 1.75mm)')
+      valid = false
+    } else {
+      setCrossSectionError('')
+    }
+    return valid
+  }
+
+  const handleSave = async () => {
+    if (!validate()) return
+    try {
+      // TODO: PUT /api/settings with { low_stock_threshold_grams, filament_cross_section_mm2, currency, theme }
+      setSaved(true)
+      setSaveError(false)
+      setTimeout(() => setSaved(false), 3000)
+    } catch {
+      setSaveError(true)
+      setSaved(false)
+    }
+  }
+
+  const testPrinterConnection = async (printer: PrinterConfig) => {
+    setPrinterStatus(s => ({ ...s, [printer.host]: 'testing' }))
+    // TODO: POST /api/printers/test with { host, type } — Dex to implement
+    await new Promise(r => setTimeout(r, 1500))
+    // Mock: hosts ending in .100 or .200 pass, others fail
+    const ok = printer.host.endsWith('.100') || printer.host.endsWith('.200')
+    setPrinterStatus(s => ({ ...s, [printer.host]: ok ? 'ok' : 'error' }))
+  }
+
+  return (
+    <div className="space-y-6 max-w-2xl">
+      {/* Header */}
+      <div className="flex flex-col sm:flex-row sm:items-center sm:justify-between gap-3">
+        <div>
+          <h2 className="text-xl font-bold text-slate-100">Settings</h2>
+          <p className="text-sm text-slate-400">App configuration for Extrudex</p>
+        </div>
+        <div className="flex items-center gap-3">
+          {saved && (
+            <span className="inline-flex items-center gap-1.5 text-sm text-emerald-400">
+              <CheckCircle2 size={16} /> Saved
+            </span>
+          )}
+          {saveError && (
+            <span className="inline-flex items-center gap-1.5 text-sm text-red-400">
+              <AlertCircle size={16} /> Save failed
+            </span>
+          )}
+          <button
+            onClick={handleSave}
+            className="inline-flex items-center gap-2 rounded-lg bg-emerald-600 px-4 py-2 text-sm font-semibold text-white hover:bg-emerald-500 active:bg-emerald-700 transition-colors"
+          >
+            <Save size={16} /> Save Settings
+          </button>
+        </div>
+      </div>
+
+      {/* Inventory Settings */}
+      <div className="rounded-lg border border-slate-700 bg-slate-800/50 px-4 pt-4 pb-2">
+        <SectionHeader
+          title="Inventory"
+          description="Controls how spools are tracked and displayed"
+        />
+        <SettingRow
+          label="Low stock threshold"
+          hint="Spools below this weight are flagged as low stock"
+        >
+          <div>
+            <div className="flex items-center gap-2">
+              <input
+                type="number"
+                min={0}
+                max={10000}
+                step={10}
+                value={lowStockThreshold}
+                onChange={e => setLowStockThreshold(Number(e.target.value))}
+                className={`w-32 rounded-lg bg-slate-800 border ${thresholdError ? 'border-red-500' : 'border-slate-700'} px-3 py-2 text-sm text-slate-100 focus:outline-none focus:ring-2 focus:ring-emerald-500`}
+              />
+              <span className="text-sm text-slate-400">grams</span>
+            </div>
+            {thresholdError && <p className="mt-1 text-xs text-red-400">{thresholdError}</p>}
+          </div>
+        </SettingRow>
+
+        <SettingRow
+          label="Filament cross-section area"
+          hint="Used to convert mm extruded → grams (π × r²)"
+        >
+          <div>
+            <div className="flex items-center gap-2">
+              <input
+                type="number"
+                min={0.01}
+                max={100}
+                step={0.001}
+                value={crossSection}
+                onChange={e => setCrossSection(Number(e.target.value))}
+                className={`w-36 rounded-lg bg-slate-800 border ${crossSectionError ? 'border-red-500' : 'border-slate-700'} px-3 py-2 text-sm text-slate-100 focus:outline-none focus:ring-2 focus:ring-emerald-500`}
+              />
+              <span className="text-sm text-slate-400">mm²</span>
+            </div>
+            {crossSectionError && <p className="mt-1 text-xs text-red-400">{crossSectionError}</p>}
+            <p className="mt-1 text-xs text-slate-500">1.75mm filament = 2.405 mm² · 2.85mm filament = 6.379 mm²</p>
+          </div>
+        </SettingRow>
+
+        <SettingRow label="Currency" hint="Used for cost display throughout the app">
+          <select
+            value={currency}
+            onChange={e => setCurrency(e.target.value)}
+            className="rounded-lg bg-slate-800 border border-slate-700 px-3 py-2 text-sm text-slate-100 focus:outline-none focus:ring-2 focus:ring-emerald-500"
+          >
+            {CURRENCIES.map(c => (
+              <option key={c} value={c}>{c}</option>
+            ))}
+          </select>
+        </SettingRow>
+      </div>
+
+      {/* Appearance */}
+      <div className="rounded-lg border border-slate-700 bg-slate-800/50 px-4 pt-4 pb-2">
+        <SectionHeader title="Appearance" />
+        <SettingRow label="Theme" hint="Override system default color scheme">
+          <div className="flex items-center gap-2">
+            {(['system', 'dark', 'light'] as const).map(t => (
+              <button
+                key={t}
+                onClick={() => setTheme(t)}
+                className={`inline-flex items-center gap-1.5 rounded-lg px-3 py-2 text-sm font-medium border transition-colors ${
+                  theme === t
+                    ? 'bg-emerald-600 border-emerald-500 text-white'
+                    : 'bg-slate-800 border-slate-700 text-slate-300 hover:bg-slate-700'
+                }`}
+              >
+                {t === 'dark' && <Moon size={14} />}
+                {t === 'light' && <Sun size={14} />}
+                {t === 'system' && <span className="text-xs">Auto</span>}
+                {t !== 'system' && <span className="capitalize">{t}</span>}
+                {t === 'system' && <span>System</span>}
+              </button>
+            ))}
+          </div>
+        </SettingRow>
+      </div>
+
+      {/* Printer Connections */}
+      <div className="rounded-lg border border-slate-700 bg-slate-800/50 px-4 pt-4 pb-2">
+        <SectionHeader
+          title="Printer Connections"
+          description="Test connectivity to configured printers"
+        />
+        {/* TODO: Load printer list from GET /api/printers */}
+        {MOCK_PRINTERS.map(printer => {
+          const status = printerStatus[printer.host] ?? 'idle'
+          return (
+            <SettingRow
+              key={printer.host}
+              label={printer.name}
+              hint={`${printer.type === 'bambu' ? 'Bambu MQTT' : 'Moonraker'} · ${printer.host}`}
+            >
+              <div className="flex items-center gap-3">
+                <StatusBadge status={status} />
+                <button
+                  onClick={() => testPrinterConnection(printer)}
+                  disabled={status === 'testing'}
+                  className="inline-flex items-center gap-1.5 rounded-lg bg-slate-700 border border-slate-600 px-3 py-1.5 text-xs font-medium text-slate-200 hover:bg-slate-600 disabled:opacity-50 disabled:cursor-not-allowed transition-colors"
+                >
+                  {status === 'testing' ? (
+                    <>
+                      <span className="animate-spin inline-block w-3 h-3 border border-slate-400 border-t-transparent rounded-full" />
+                      Testing…
+                    </>
+                  ) : (
+                    <>
+                      <Wifi size={12} /> Test Connection
+                    </>
+                  )}
+                </button>
+              </div>
+            </SettingRow>
+          )
+        })}
+      </div>
+
+      {/* Save footer (mobile convenience) */}
+      <div className="flex justify-end pb-4">
+        <button
+          onClick={handleSave}
+          className="inline-flex items-center gap-2 rounded-lg bg-emerald-600 px-5 py-2.5 text-sm font-semibold text-white hover:bg-emerald-500 active:bg-emerald-700 transition-colors"
+        >
+          <Save size={16} /> Save Settings
+        </button>
+      </div>
+    </div>
+  )
+}
+
+function StatusBadge({ status }: { status: ConnectionStatus }) {
+  if (status === 'idle') return null
+  if (status === 'testing') {
+    return (
+      <span className="inline-flex items-center gap-1 rounded-full bg-slate-700 border border-slate-600 px-2 py-0.5 text-xs text-slate-300">
+        Testing…
+      </span>
+    )
+  }
+  if (status === 'ok') {
+    return (
+      <span className="inline-flex items-center gap-1 rounded-full bg-emerald-900/30 border border-emerald-700 px-2 py-0.5 text-xs text-emerald-300">
+        <CheckCircle2 size={11} /> Connected
+      </span>
+    )
+  }
+  return (
+    <span className="inline-flex items-center gap-1 rounded-full bg-red-900/30 border border-red-700 px-2 py-0.5 text-xs text-red-300">
+      <WifiOff size={11} /> Unreachable
+    </span>
+  )
+}

frontend/src/services/printerService.ts

@@ -1,13 +0,0 @@
-import axios from 'axios'
-import type { Printer } from '../types/printer'
-
-const API_BASE = '/api'
-
-export async function fetchPrinters(): Promise<Printer[]> {
-  const res = await axios.get<{ data: Printer[] }>(`${API_BASE}/printers`)
-  return res.data.data
-}
-
-export async function deletePrinter(id: number): Promise<void> {
-  await axios.delete(`${API_BASE}/printers/${id}`)
-}

frontend/src/types/printer.ts

@@ -1,33 +0,0 @@
-// Extrudex printer domain types
-
-export interface PrinterType {
-  id: number
-  name: string
-  created_at: string
-  updated_at: string
-}
-
-export interface Printer {
-  id: number
-  name: string
-  printer_type_id: number
-  printer_type?: PrinterType
-  manufacturer?: string
-  model?: string
-  moonraker_url?: string
-  moonraker_api_key?: string
-  mqtt_broker_host?: string
-  mqtt_topic_prefix?: string
-  mqtt_tls_enabled: boolean
-  is_active: boolean
-  connection_status?: 'online' | 'offline' | 'unknown'
-  created_at: string
-  updated_at: string
-}
-
-export interface ListResponse<T> {
-  data: T[]
-  total: number
-  limit: number
-  offset: number
-}