chore(main): initialize and register SystemSettingsHandler

Add SystemSettingsHandler initialization in main.go:
- Create systemSettingsHandler instance with queries
- Add to router.Config for route registration
- Properly wired with existing dependencies

This enables the system settings endpoints to be registered and functional.

cmd/server/main.go

@@ -82,6 +82,7 @@ func main() {
 	loginAttemptTracker := ratelimit.NewLoginAttemptTracker(5, 15*time.Minute, 5*time.Minute)
 
 	authHandler := handlers.NewAuthHandler(queries, cfg.JWTSecret, loginAttemptTracker)
+	systemSettingsHandler := handlers.NewSystemSettingsHandler(queries)
 	libraryHandler := handlers.NewLibraryHandler(queries)
 	deviceHandler := handlers.NewDeviceHandler(queries, cfg.JWTSecret, cfg)
 	deviceAuthMiddleware := middleware.NewDeviceAuthMiddleware(queries)
@@ -145,27 +146,28 @@ func main() {
 	// ROUTER REGISTRATION - Migrate routes to internal/router/ package
 	// ========================================================================
 	routerConfig := &router.Config{
-		Echo:                 e,
-		Queries:              queries,
-		Cfg:                  cfg,
-		DBPool:               dbPool,
-		AuthHandler:          authHandler,
-		LibraryHandler:       libraryHandler,
-		DeviceHandler:        deviceHandler,
-		MediaHandler:         mediaHandler,
-		SearchHandler:        searchHandler,
-		MatchingHandler:      matchingHandler,
-		KOReaderHandler:      koreaderHandler,
-		WSHandler:            wsHandler,
-		ConflictHandler:      conflictHandler,
-		AnalyticsHandler:     analyticsHandler,
-		QueueHandler:         queueHandler,
-		CollectionHandler:    collectionHandler,
-		OPDSHandler:          opdsHandler,
-		ConnManager:          connManager,
-		QueueProcessor:       queueProcessor,
-		DeviceAuthMiddleware: deviceAuthMiddleware,
-		LoginTracker:         loginAttemptTracker,
+		Echo:                  e,
+		Queries:               queries,
+		Cfg:                   cfg,
+		DBPool:                dbPool,
+		AuthHandler:           authHandler,
+		LibraryHandler:        libraryHandler,
+		DeviceHandler:         deviceHandler,
+		MediaHandler:          mediaHandler,
+		SearchHandler:         searchHandler,
+		MatchingHandler:       matchingHandler,
+		KOReaderHandler:       koreaderHandler,
+		WSHandler:             wsHandler,
+		ConflictHandler:       conflictHandler,
+		AnalyticsHandler:      analyticsHandler,
+		QueueHandler:          queueHandler,
+		CollectionHandler:     collectionHandler,
+		OPDSHandler:           opdsHandler,
+		SystemSettingsHandler: systemSettingsHandler,
+		ConnManager:           connManager,
+		QueueProcessor:        queueProcessor,
+		DeviceAuthMiddleware:  deviceAuthMiddleware,
+		LoginTracker:          loginAttemptTracker,
 	}
 
 	// Register all routes and get ebook handler