feat: add team calendar ICS endpoint and related functionality

- Implemented a new API endpoint to generate an ICS calendar for team duty shifts, accessible via a valid token.
- Enhanced the `calendar_link` command to return both personal and team calendar URLs.
- Added a new function to build the team ICS file, ensuring each event includes the duty holder's name in the description.
- Updated tests to cover the new team calendar functionality, including validation for token formats and response content.
- Revised internationalization messages to reflect the new team calendar links.

tests/test_app.py

@@ -268,6 +268,67 @@ def test_duties_200_with_unknown_event_type_mapped_to_duty(client):
     assert data[0]["full_name"] == "User A"
 
 
+def test_calendar_ical_team_404_invalid_token_format(client):
+    """GET /api/calendar/ical/team/{token}.ics with invalid token format returns 404 without DB."""
+    r = client.get("/api/calendar/ical/team/short.ics")
+    assert r.status_code == 404
+    assert "not found" in r.text.lower()
+
+
+@patch("duty_teller.api.app.get_user_by_calendar_token")
+def test_calendar_ical_team_404_unknown_token(mock_get_user, client):
+    """GET /api/calendar/ical/team/{token}.ics with unknown token returns 404."""
+    mock_get_user.return_value = None
+    valid_format_token = "B" * 43
+    r = client.get(f"/api/calendar/ical/team/{valid_format_token}.ics")
+    assert r.status_code == 404
+    assert "not found" in r.text.lower()
+    mock_get_user.assert_called_once()
+
+
+@patch("duty_teller.api.app.build_team_ics")
+@patch("duty_teller.api.app.get_duties")
+@patch("duty_teller.api.app.get_user_by_calendar_token")
+def test_calendar_ical_team_200_only_duty_and_description(
+    mock_get_user, mock_get_duties, mock_build_team_ics, client
+):
+    """GET /api/calendar/ical/team/{token}.ics returns ICS with duty-only events and DESCRIPTION."""
+    from types import SimpleNamespace
+
+    mock_user = SimpleNamespace(id=1, full_name="User A")
+    mock_get_user.return_value = mock_user
+    duty = SimpleNamespace(
+        id=10,
+        user_id=1,
+        start_at="2026-06-15T09:00:00Z",
+        end_at="2026-06-15T18:00:00Z",
+        event_type="duty",
+    )
+    non_duty = SimpleNamespace(
+        id=11,
+        user_id=2,
+        start_at="2026-06-16T09:00:00Z",
+        end_at="2026-06-16T18:00:00Z",
+        event_type="vacation",
+    )
+    mock_get_duties.return_value = [(duty, "User A"), (non_duty, "User B")]
+    mock_build_team_ics.return_value = b"BEGIN:VCALENDAR\r\nPRODID:Team\r\nVEVENT\r\nDESCRIPTION:User A\r\nEND:VCALENDAR"
+    token = "y" * 43
+
+    r = client.get(f"/api/calendar/ical/team/{token}.ics")
+    assert r.status_code == 200
+    assert r.headers.get("content-type", "").startswith("text/calendar")
+    assert b"BEGIN:VCALENDAR" in r.content
+    mock_get_user.assert_called_once()
+    mock_get_duties.assert_called_once()
+    # build_team_ics called with only duty (event_type duty), not vacation
+    mock_build_team_ics.assert_called_once()
+    duties_arg = mock_build_team_ics.call_args[0][0]
+    assert len(duties_arg) == 1
+    assert duties_arg[0][0].event_type == "duty"
+    assert duties_arg[0][1] == "User A"
+
+
 def test_calendar_ical_404_invalid_token_format(client):
     """GET /api/calendar/ical/{token}.ics with invalid token format returns 404 without DB call."""
     # Token format must be base64url, 40–50 chars; short or invalid chars → 404