feat: add tests for admin checks and error handling

- Introduced new tests for the `is_admin_async` function to verify correct behavior based on user roles.
- Added tests for error handling in the `error_handler` to ensure exceptions are logged and do not propagate.
- Enhanced test coverage for configuration settings by adding a test for parsing admin phone numbers from environment variables.
- Updated the `.cursorrules` file to include the use of a virtual environment for better dependency management.

tests/test_personal_calendar_ics.py

@@ -58,3 +58,19 @@ def test_build_personal_ics_event_types():
     summaries = [str(ev.get("summary")) for ev in events]
     assert "Unavailable" in summaries
     assert "Vacation" in summaries
+
+
+def test_build_personal_ics_naive_datetime_treated_as_utc():
+    """Duties with start_at/end_at without Z (naive datetime) are treated as UTC."""
+    duties = [
+        _duty(1, "2025-02-20T09:00:00", "2025-02-20T18:00:00", "duty"),
+    ]
+    ics = build_personal_ics(duties)
+    cal = ICalendar.from_ical(ics)
+    assert cal is not None
+    events = [c for c in cal.walk() if c.name == "VEVENT"]
+    assert len(events) == 1
+    ev = events[0]
+    assert ev.get("summary") == "Duty"
+    assert "2025-02-20" in str(ev.get("dtstart").dt)
+    assert "2025-02-20" in str(ev.get("dtend").dt)