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.

internal/router/router.go

@@ -83,7 +83,7 @@ func createJWTMiddleware(cfg *Config) echo.MiddlewareFunc {
 }
 
 // RegisterRoutes registers all application routes
-func RegisterRoutes(cfg *Config) {
+func RegisterRoutes(cfg *Config) *handlers.Handler {
 	e := cfg.Echo
 
 	// Set up validator
@@ -111,7 +111,7 @@ func RegisterRoutes(cfg *Config) {
 	// Register core application routes (collections, devices, media, etc.) - ONCE
 	jwtMiddleware := createJWTMiddleware(cfg)
 	protected := e.Group("/api", jwtMiddleware)
-	handlers.SetupRoutes(protected, cfg.Queries, cfg.ConnManager)
+	ebookHandler := handlers.SetupRoutes(protected, cfg.Queries, cfg.ConnManager)
 
 	// Register route groups
 	registerAuthRoutes(cfg, rateLimitMiddleware)
@@ -126,4 +126,10 @@ func RegisterRoutes(cfg *Config) {
 	registerWebSocketRoutes(cfg)
 	registerFrontendRoutes(cfg)
 	registerDocumentationRoutes(cfg)
+
+	// Register scanner routes (admin only)
+	admin := protected.Group("", handlers.AdminMiddleware)
+	registerScannerRoutes(admin, ebookHandler)
+
+	return ebookHandler
 }