chore: clean up pre-existing ruff violations in tests

Remove unused imports (F401) and strip trailing whitespace (W291/W293) flagged
by ruff in test files. Pre-existing debt unrelated to any single feature; CI runs
pytest but not ruff, so these had accumulated. No behavior change.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NGzHtDvJur9U7ysgRKRUTN

tests/test_events.py

@@ -112,7 +112,7 @@ def test_add_event_posts_when_no_event_id(monkeypatch):
     rec = _patch(monkeypatch, lambda _k: {"id": "e99"})
     out = _run(
         events.add_or_update_event(
-            workout_type="Ride", name="Threshold", 
+            workout_type="Ride", name="Threshold",
             start_date="2026-07-10", moving_time=3600, distance=40000,
             workout_doc=WorkoutDoc(description="d", steps=[Step(duration=600)]),
         )
@@ -128,7 +128,7 @@ def test_update_event_puts_when_event_id(monkeypatch):
     rec = _patch(monkeypatch, lambda _k: {"id": "e5"})
     _run(
         events.add_or_update_event(
-            workout_type="Ride", name="Threshold", 
+            workout_type="Ride", name="Threshold",
             event_id="e5", start_date="2026-07-10",
         )
     )