CUB-113: implement core CRUD API endpoints

- Add dtos package with request/response structs
- Add repositories: Material, Filament, Printer, PrintJob, UsageLog
- Add services: FilamentService, PrinterService, PrintJobService
- Add handlers for all 5 resources with consistent error responses
- Wire all endpoints into Chi router under /api
- Validation on POST/PUT filament endpoints
- Filter/pagination support on list endpoints
- Soft-delete for filaments (DELETE /api/filaments/{id})
- go build ./... && go vet ./... → PASS

backend/internal/router/router.go

@@ -1,12 +1,13 @@
 package router
 
 import (
-	"log/slog"
 	"net/http"
 	"time"
 
 	"github.com/CubeCraft-Creations/Extrudex/backend/internal/config"
 	"github.com/CubeCraft-Creations/Extrudex/backend/internal/handlers"
+	"github.com/CubeCraft-Creations/Extrudex/backend/internal/repositories"
+	"github.com/CubeCraft-Creations/Extrudex/backend/internal/services"
 	"github.com/go-chi/chi/v5"
 	"github.com/go-chi/chi/v5/middleware"
 	"github.com/jackc/pgx/v5/pgxpool"
@@ -41,5 +42,43 @@ func New(cfg *config.Config, dbPool *pgxpool.Pool) chi.Router {
 	healthHandler := handlers.NewHealthHandler(dbPool)
 	r.Get("/health", healthHandler.ServeHTTP)
 
+	// ── Repositories ──────────────────────────────────────────────────────
+	materialRepo := repositories.NewMaterialRepository(dbPool)
+	filamentRepo := repositories.NewFilamentRepository(dbPool)
+	printerRepo := repositories.NewPrinterRepository(dbPool)
+	printJobRepo := repositories.NewPrintJobRepository(dbPool)
+	usageLogRepo := repositories.NewUsageLogRepository(dbPool)
+
+	// ── Services ──────────────────────────────────────────────────────────
+	filamentService := services.NewFilamentService(filamentRepo)
+	printerService := services.NewPrinterService(printerRepo)
+	printJobService := services.NewPrintJobService(printJobRepo)
+
+	// ── Handlers ──────────────────────────────────────────────────────────
+	materialHandler := handlers.NewMaterialHandler(materialRepo)
+	filamentHandler := handlers.NewFilamentHandler(filamentService)
+	printerHandler := handlers.NewPrinterHandler(printerService)
+	printJobHandler := handlers.NewPrintJobHandler(printJobService)
+	usageLogHandler := handlers.NewUsageLogHandler(usageLogRepo)
+
+	// ── API Routes ────────────────────────────────────────────────────────
+	r.Route("/api", func(r chi.Router) {
+		r.Get("/materials", materialHandler.List)
+
+		r.Route("/filaments", func(r chi.Router) {
+			r.Get("/", filamentHandler.List)
+			r.Post("/", filamentHandler.Create)
+			r.Route("/{id}", func(r chi.Router) {
+				r.Get("/", filamentHandler.Get)
+				r.Put("/", filamentHandler.Update)
+				r.Delete("/", filamentHandler.Delete)
+			})
+		})
+
+		r.Get("/printers", printerHandler.List)
+		r.Get("/print-jobs", printJobHandler.List)
+		r.Get("/usage-logs", usageLogHandler.List)
+	})
+
 	return r
 }