feat(scanner): restore auto-start functionality for scheduler and watch mode

Phase 1 of scanner restoration plan

Changes:
- cmd/server/main.go: Capture ebookHandler from router.RegisterRoutes
- cmd/server/main.go: Start scheduler in background goroutine
- cmd/server/main.go: Defer StopScheduler() for graceful shutdown
- cmd/server/main.go: Start watch mode for all libraries after 2-second delay
- internal/router/router.go: Return ebookHandler from RegisterRoutes

This restores critical functionality that was removed during router refactor:
- Auto-scanning now works again
- Watch mode starts automatically for all libraries
- Graceful shutdown properly stops scheduler

Fixes issue where scheduler and watch mode were not starting on server boot.

cmd/server/main.go

@@ -148,7 +148,25 @@ func main() {
 		DeviceAuthMiddleware: deviceAuthMiddleware,
 		LoginTracker:         loginAttemptTracker,
 	}
-	router.RegisterRoutes(routerConfig)
+
+	// Register all routes and get ebook handler
+	ebookHandler := router.RegisterRoutes(routerConfig)
+
+	// ========================================================================
+	// BACKGROUND SERVICES - Restore auto-start functionality
+	// ========================================================================
+
+	// Start scheduler for auto-scanning
+	go ebookHandler.StartScheduler()
+	defer ebookHandler.StopScheduler()
+
+	// Start watch mode for all libraries (background)
+	go func() {
+		time.Sleep(2 * time.Second) // Wait for server to be ready
+		if err := ebookHandler.StartWatchModeForAllLibraries(context.Background()); err != nil {
+			log.Printf("Warning: failed to start watch mode for libraries: %v", err)
+		}
+	}()
 
 	// Public library types endpoint (no authentication required)
 	e.GET("/api/libraries/types", libraryHandler.GetLibraryTypes)