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/lora_manager.py

@@ -190,6 +190,9 @@ class LoraManager:
 
             # Register DownloadManager with ServiceRegistry
             await ServiceRegistry.get_download_manager()
+
+            from .services.metadata_service import initialize_metadata_providers
+            await initialize_metadata_providers()
             
             # Initialize WebSocket manager
             await ServiceRegistry.get_websocket_manager()