feat(metadata): implement metadata providers and initialize metadata service

- Added ModelMetadataProvider and CivitaiModelMetadataProvider for handling model metadata.
- Introduced SQLiteModelMetadataProvider for SQLite database integration.
- Created metadata_service.py to initialize and configure metadata providers.
- Updated CivitaiClient to register as a metadata provider.
- Refactored download_manager to use the new download_file method.
- Added SQL schema for models, model_versions, and model_files.
- Updated requirements.txt to include aiosqlite.

py/utils/routes_common.py

@@ -13,6 +13,7 @@ from ..utils.exif_utils import ExifUtils
 from ..utils.metadata_manager import MetadataManager
 from ..services.download_manager import DownloadManager
 from ..services.websocket_manager import ws_manager
+from ..services.metadata_service import get_metadata_provider
 
 logger = logging.getLogger(__name__)