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.

duty_teller/api/personal_calendar_ics.py

@@ -50,3 +50,39 @@ def build_personal_ics(duties_with_name: list[tuple[Duty, str]]) -> bytes:
         cal.add_component(event)
 
     return cal.to_ical()
+
+
+def build_team_ics(duties_with_name: list[tuple[Duty, str]]) -> bytes:
+    """Build a VCALENDAR (ICS) with one VEVENT per duty for team calendar.
+
+    Same structure as personal calendar; PRODID is Team Calendar; each VEVENT
+    has SUMMARY='Duty' and DESCRIPTION set to the duty holder's full_name.
+
+    Args:
+        duties_with_name: List of (Duty, full_name). full_name is used for DESCRIPTION.
+
+    Returns:
+        ICS file content as bytes (UTF-8).
+    """
+    cal = Calendar()
+    cal.add("prodid", "-//Duty Teller//Team Calendar//EN")
+    cal.add("version", "2.0")
+    cal.add("calscale", "GREGORIAN")
+
+    for duty, full_name in duties_with_name:
+        event = Event()
+        start_dt = parse_utc_iso(duty.start_at)
+        end_dt = parse_utc_iso(duty.end_at)
+        if start_dt.tzinfo is None:
+            start_dt = start_dt.replace(tzinfo=timezone.utc)
+        if end_dt.tzinfo is None:
+            end_dt = end_dt.replace(tzinfo=timezone.utc)
+        event.add("dtstart", start_dt)
+        event.add("dtend", end_dt)
+        event.add("summary", "Duty")
+        event.add("description", full_name)
+        event.add("uid", f"duty-{duty.id}@duty-teller")
+        event.add("dtstamp", datetime.now(timezone.utc))
+        cal.add_component(event)
+
+    return cal.to_ical()