style: apply ruff fixes

backend/tests/test_ask.py

@@ -1,11 +1,7 @@
 from datetime import UTC, datetime, timedelta
 
-import pytest
-from fastapi.testclient import TestClient
-
 from routes.ask import _build_event_query, _extract_entity, _extract_time_range
 
-
 # ---------------------------------------------------------------------------
 # Unit tests: time-range extraction
 # ---------------------------------------------------------------------------
@@ -44,7 +40,7 @@ class TestExtractTimeRange:
     def test_today(self):
         start, end = _extract_time_range("What happened today?")
         start_dt = datetime.fromisoformat(start.replace("Z", "+00:00"))
-        end_dt = datetime.fromisoformat(end.replace("Z", "+00:00"))
+        # end_dt is not needed for this assertion
         # Should be from midnight today to now
         assert start_dt.hour == 0
         assert start_dt.minute == 0