test(audit): the day-group fixture is a def, not a lambda (ruff E731)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/core/test_audit_page.py

@@ -114,7 +114,10 @@ def test_dividers_open_each_day_group_once_even_across_pages():
     dividers, with every row's own date beside it."""
     from steward.audit.service import mark_day_groups
     now = datetime(2026, 10, 8, 18, 0, tzinfo=timezone.utc)
-    at = lambda d, h=12: NS(timestamp=datetime(2026, 10, d, h, 0, tzinfo=timezone.utc))
+
+    def at(d, h=12):
+        return NS(timestamp=datetime(2026, 10, d, h, 0, tzinfo=timezone.utc))
+
     page1 = [{"event": at(8)}, {"event": at(8, 9)}, {"event": at(7)}, {"event": at(5)}]
     assert mark_day_groups(page1, timezone.utc, "", now) == "Last 7 days"
     assert [(i["group"], i["opens_group"]) for i in page1] == [