fix: improve maintenance and synchronize live conversations

backend/app/api/file_upload.py

@@ -14,20 +14,17 @@ See the License for the specific language governing permissions and
 limitations under the License.
 """
 
-from fastapi import APIRouter, UploadFile, File, HTTPException, Depends, status, Header, Request, Query
-from fastapi.responses import FileResponse, JSONResponse
+from fastapi import APIRouter, HTTPException, Depends, status, Header, Request, Query
+from fastapi.responses import FileResponse
 from typing import Optional, Tuple
 import uuid
 import os
-from datetime import datetime
 from urllib.parse import quote
 from sqlalchemy.orm import Session
 from app.core.config import settings
-from app.core.s3 import upload_file_to_s3, get_s3_signed_url
 from app.core.local_file_urls import verify_local_signature
 from app.core.logger import get_logger
 from app.core.security import verify_conversation_token
-from app.models import User
 from app.core.auth import get_current_user
 from app.database import get_db