fix: auto-fix code issues (cron)

- 修复重复导入/字段
- 修复异常处理
- 修复PEP8格式问题
- 添加类型注解

backend/main.py

@@ -10,6 +10,7 @@ import io
 import json
 import logging
 import os
+import re
 import sys
 import time
 import uuid
@@ -19,7 +20,7 @@ from typing import Any, Optional
 import httpx
 from fastapi import Body, Depends, FastAPI, File, Form, Header, HTTPException, Query, Request, UploadFile
 from fastapi.middleware.cors import CORSMiddleware
-from fastapi.responses import JSONResponse, StreamingResponse
+from fastapi.responses import JSONResponse, PlainTextResponse, StreamingResponse
 from fastapi.staticfiles import StaticFiles
 from pydantic import BaseModel, Field