CUB-121: build React pages with real API integration

- HubPage: agent summary stats, cards, status badges, progress bars, refresh
- LogsPage: activity feed from tasks, status filter, loading skeleton
- ProjectsPage: project cards with status badges and agent counts
- SessionsPage: responsive table/card view with model/token info
- SettingsPage: dark mode toggle, gateway URL, refresh interval persist
- ThemeProvider with dark/light mode via CSS custom properties
- useLocalStorage hook for settings persistence
- Loading/error/empty states across all pages
- npm run build passes cleanly

frontend/src/pages/SettingsPage.tsx

@@ -1,8 +1,126 @@
+import { useTheme } from '../hooks/useTheme'
+import { useLocalStorage } from '../hooks/useLocalStorage'
+import { Sun, Moon, Monitor, Zap, Clock } from 'lucide-react'
+
+const REFRESH_PRESETS = [
+  { label: '5s', value: 5_000 },
+  { label: '10s', value: 10_000 },
+  { label: '30s', value: 30_000 },
+  { label: '60s', value: 60_000 },
+]
+
 export default function SettingsPage() {
+  const { isDark, toggleTheme } = useTheme()
+  const [gatewayUrl, setGatewayUrl] = useLocalStorage('cc-gateway-url', '')
+  const [refreshInterval, setRefreshInterval] = useLocalStorage('cc-refresh-interval', 30_000)
+
   return (
-    <div>
-      <h1 className="text-2xl font-bold mb-4">Settings</h1>
-      <p className="text-on-surface-variant">System settings will appear here.</p>
+    <div className="space-y-8 max-w-2xl">
+      <header>
+        <h1 className="text-2xl font-bold">Settings</h1>
+        <p className="text-on-surface-variant">Application preferences</p>
+      </header>
+
+      {/* Appearance */}
+      <section className="space-y-4">
+        <h2 className="text-lg font-semibold flex items-center gap-2">
+          <Monitor size={20} className="text-primary" />
+          Appearance
+        </h2>
+
+        <div className="p-5 rounded-xl border border-surface-light bg-surface-dark">
+          <div className="flex items-center justify-between">
+            <div>
+              <p className="font-medium">Dark Mode</p>
+              <p className="text-sm text-on-surface-variant">Toggle between dark and light themes</p>
+            </div>
+            <button
+              onClick={toggleTheme}
+              className={`relative w-14 h-8 rounded-full transition-colors duration-200 ${
+                isDark ? 'bg-primary' : 'bg-surface-lighter'
+              }`}
+              aria-label="Toggle dark mode"
+            >
+              <div
+                className={`absolute top-1 h-6 w-6 rounded-full bg-white transition-transform duration-200 flex items-center justify-center ${
+                  isDark ? 'translate-x-7' : 'translate-x-1'
+                }`}
+              >
+                {isDark ? <Moon size={14} className="text-surface-darkest" /> : <Sun size={14} className="text-yellow-500" />}
+              </div>
+            </button>
+          </div>
+        </div>
+      </section>
+
+      {/* Connection */}
+      <section className="space-y-4">
+        <h2 className="text-lg font-semibold flex items-center gap-2">
+          <Zap size={20} className="text-primary" />
+          Connection
+        </h2>
+
+        <div className="p-5 rounded-xl border border-surface-light bg-surface-dark space-y-3">
+          <div>
+            <label htmlFor="gateway-url" className="block text-sm font-medium mb-1">
+              Gateway URL
+            </label>
+            <input
+              id="gateway-url"
+              type="url"
+              value={gatewayUrl}
+              onChange={(e) => setGatewayUrl(e.target.value)}
+              placeholder="http://localhost:8080"
+              className="w-full px-3 py-2 rounded-lg border border-surface-light bg-surface-darkest text-on-surface placeholder:text-on-surface-muted focus:outline-none focus:ring-2 focus:ring-primary/50 focus:border-primary transition-colors"
+            />
+            <p className="text-xs text-on-surface-muted mt-1">
+              The backend Gateway address for API requests
+            </p>
+          </div>
+        </div>
+      </section>
+
+      {/* Refresh */}
+      <section className="space-y-4">
+        <h2 className="text-lg font-semibold flex items-center gap-2">
+          <Clock size={20} className="text-primary" />
+          Auto Refresh
+        </h2>
+
+        <div className="p-5 rounded-xl border border-surface-light bg-surface-dark space-y-3">
+          <p className="text-sm text-on-surface-variant">Data refresh interval for agent status and logs</p>
+
+          <div className="flex flex-col gap-2">
+            <input
+              type="range"
+              min="0"
+              max="3"
+              step="1"
+              value={REFRESH_PRESETS.findIndex((p) => p.value === refreshInterval)}
+              onChange={(e) => {
+                const idx = parseInt(e.target.value)
+                setRefreshInterval(REFRESH_PRESETS[idx].value)
+              }}
+              className="w-full accent-primary"
+            />
+            <div className="flex justify-between text-xs text-on-surface-muted">
+              {REFRESH_PRESETS.map((p) => (
+                <button
+                  key={p.label}
+                  onClick={() => setRefreshInterval(p.value)}
+                  className={`px-3 py-1 rounded-lg transition-colors ${
+                    refreshInterval === p.value
+                      ? 'bg-primary/10 text-primary'
+                      : 'hover:bg-surface-light'
+                  }`}
+                >
+                  {p.label}
+                </button>
+              ))}
+            </div>
+          </div>
+        </div>
+      </section>
     </div>
   )
 }