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/middleware/middleware.py

@@ -34,6 +34,7 @@ class AuthMiddleware(BaseHTTPMiddleware):
             and not request.url.path.startswith("/openai")
             and not request.url.path.startswith("/api/version/check")
             and not request.url.path.startswith("/vertex-express")
+            and not request.url.path.startswith("/upload")
         ):
 
             auth_token = request.cookies.get("auth_token")