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)
@@ -162,6 +163,7 @@ func main() {
 		QueueHandler:          queueHandler,
 		CollectionHandler:     collectionHandler,
 		OPDSHandler:           opdsHandler,
+		SystemSettingsHandler: systemSettingsHandler,
 		ConnManager:           connManager,
 		QueueProcessor:        queueProcessor,
 		DeviceAuthMiddleware:  deviceAuthMiddleware,