Fix NameError: restore File import removed during 422 fix

routes/conversation.py

@@ -12,7 +12,7 @@ from pathlib import Path
 
 import requests
 from typing import Optional
-from fastapi import APIRouter, Form, HTTPException, Request, UploadFile
+from fastapi import APIRouter, File, Form, HTTPException, Request, UploadFile
 from fastapi.responses import Response, StreamingResponse
 
 from core.config import _load_settings, _save_settings, _clean_preview_backend