fix: restore missing FastAPI and Typing imports in app_hf.py

backend/app_hf.py

@@ -13,8 +13,15 @@ import uuid
 import asyncio
 import logging
 import sys
-import os
 from pathlib import Path
+from concurrent.futures import ThreadPoolExecutor
+from typing import Any, Dict
+
+from fastapi import FastAPI, UploadFile, File, HTTPException, WebSocket, WebSocketDisconnect
+from fastapi.responses import FileResponse, JSONResponse
+from fastapi.staticfiles import StaticFiles
+from fastapi.middleware.cors import CORSMiddleware
+
 # Add current directory to path so relative imports work without package structure
 sys.path.append(os.path.dirname(os.path.abspath(__file__)))