feat: Add Files API support with upload, list, get and delete operations

- Implement complete Files API compatible with Gemini API format
- Support resumable file uploads with chunked transfer (tested with 15MB video)
- Create file management service with database tracking
- Add file domain models and API request/response objects
- Implement file routes with proper authentication
- Use fixed API key for Files API requests (due to Google API restrictions)
- Support file state management (PROCESSING, ACTIVE, FAILED)
- Add scheduled task for automatic expired file cleanup
- Integrate seamlessly with existing key management and load balancing

app/config/config.py

@@ -123,6 +123,10 @@ class Settings(BaseSettings):
     AUTO_DELETE_REQUEST_LOGS_DAYS: int = 30
     SAFETY_SETTINGS: List[Dict[str, str]] = DEFAULT_SAFETY_SETTINGS
 
+    # Files API
+    FILES_CLEANUP_ENABLED: bool = True
+    FILES_CLEANUP_INTERVAL_HOURS: int = 1
+    FILES_USER_ISOLATION_ENABLED: bool = True
 
     def __init__(self, **kwargs):
         super().__init__(**kwargs)