fix(desktop): opc.py 补导入 HTTPException，修复 permissions/me 转发 401 时 NameError→500

未登录时 /api/permissions/me 转发返回 401，forward() 抛 HTTPException，
但 except HTTPException 未导入导致 NameError，掩盖了真实的 401 并变成 500。

src/pineagents/app/routers/opc.py

@@ -10,7 +10,7 @@ import logging
 import time
 from typing import Any
 
-from fastapi import APIRouter, Request, UploadFile, File
+from fastapi import APIRouter, HTTPException, Request, UploadFile, File
 from pydantic import BaseModel
 
 from ..server_client import forward, forward_upload