fix(calendar): accept time-first datetimes in _parse_dt

Accept calendar datetime phrases such as "3pm tomorrow" by adding a time-first natural-language parser branch mirroring the reminder parser. Add regression coverage proving time-first forms match their existing day-first equivalents.

tests/test_calendar_parse_dt_time_first.py

@@ -0,0 +1,31 @@
+"""Regression: _parse_dt must understand "time-first" phrasings like parse_due_for_user does.
+
+parse_due_for_user accepts both day-first ("tomorrow at 9am") and time-first
+("9am tomorrow") forms, but _parse_dt (the parser _parse_dt_pair falls back to
+for calendar event start/end) only handled the day-first form. A time-first
+start like "3pm tomorrow" missed every branch and fell through to dateutil,
+which raises ParserError on "3pm tomorrow", so creating an event with that
+phrasing failed. Time-first is now handled identically to its day-first
+equivalent, mirroring the sibling reminder parser.
+"""
+from routes.calendar_routes import _parse_dt
+
+
+def test_time_first_today_equals_day_first():
+    assert _parse_dt("3pm today") == _parse_dt("today at 3pm")
+
+
+def test_time_first_tomorrow_equals_day_first():
+    assert _parse_dt("9am tomorrow") == _parse_dt("tomorrow at 9am")
+
+
+def test_time_first_with_minutes_equals_day_first():
+    assert _parse_dt("2:30pm tomorrow") == _parse_dt("tomorrow at 2:30pm")
+
+
+def test_time_first_tonight_maps_to_today():
+    assert _parse_dt("11pm tonight") == _parse_dt("today at 11pm")
+
+
+def test_time_first_yesterday_equals_day_first():
+    assert _parse_dt("8am yesterday") == _parse_dt("yesterday at 8am")