fix: remove unused os import in conversation/tools.py

Left dangling after the exec-aide-reminder removal (INFRA-37); ruff F401.

INFRA-37

src/conversation/tools.py

@@ -1,6 +1,5 @@
 import json
 import logging
-import os
 from datetime import datetime, timezone
 
 import boto3
@@ -614,7 +613,6 @@ def _handle_delete_task(inputs):
     return {"task_id": inputs["task_id"], "status": "deleted"}
 
 
-
 # ── Calendar Handlers ──────────────────────────────────────────