fix(ai): ruff 自动修复 health 模块

services/ai/src/health/health.py

@@ -9,7 +9,8 @@
     from health import router as health_router
     app.include_router(health_router)
 """
-from datetime import datetime, timezone
+
+from datetime import UTC, datetime
 
 from fastapi import APIRouter
 
@@ -32,5 +33,5 @@ async def readyz() -> dict:
     return {
         "status": "ok",
         "service": SERVICE_NAME,
-        "timestamp": datetime.now(timezone.utc).isoformat(),
+        "timestamp": datetime.now(UTC).isoformat(),
     }