Add sync_single_series_after_scan with NFO metadata and WebSocket updates

- Implement sync_single_series_after_scan to persist scanned series to database
- Enhanced _broadcast_series_updated to include full NFO metadata (nfo_created_at, nfo_updated_at, tmdb_id, tvdb_id)
- Add immediate episode scanning in add_series endpoint when background loader isn't running
- Implement updateSingleSeries in frontend to handle series_updated WebSocket events
- Add SERIES_UPDATED event constant to WebSocket event definitions
- Update background loader to use sync_single_series_after_scan method
- Simplified background loader initialization in FastAPI app
- Add comprehensive tests for series update WebSocket payload and episode counting logic
- Import reorganization: move get_background_loader_service to dependencies module

src/server/fastapi_app.py

@@ -251,17 +251,9 @@ async def lifespan(_application: FastAPI):
                 logger.info("Download service initialized and queue restored")
                 
                 # Initialize background loader service
-                from src.server.services.background_loader_service import (
-                    init_background_loader_service,
-                )
-                from src.server.utils.dependencies import get_series_app
+                from src.server.utils.dependencies import get_background_loader_service
                 
-                series_app_instance = get_series_app()
-                background_loader = init_background_loader_service(
-                    websocket_service=ws_service,
-                    anime_service=anime_service,
-                    series_app=series_app_instance
-                )
+                background_loader = get_background_loader_service()
                 await background_loader.start()
                 initialized['background_loader'] = True
                 logger.info("Background loader service started")