fix migration

backend/app/llm/client.py

@@ -19,6 +19,9 @@ class LLMClient:
             base_url=settings.openrouter_base_url,
         )
 
+    async def aclose(self) -> None:
+        await self.client.close()
+
     def _runtime(self) -> tuple[str, str, str]:
         from app.db.base import SessionLocal
         from app.settings.service import SettingsService