hotfix: 补充 product_service.py 顶部缺失的 func 导入

backend/app/services/product_service.py

@@ -2,7 +2,7 @@
 from __future__ import annotations
 import uuid
 from fastapi import HTTPException, status
-from sqlalchemy import select, or_, cast, String, delete, update
+from sqlalchemy import select, or_, cast, String, delete, update, func
 from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy.orm import selectinload