refactor: simplify ICS calendar API to return only duty shifts

- Removed the ability to specify multiple event types in the ICS calendar generation API, ensuring it only returns duty shifts.
- Updated the associated test to reflect the change in behavior, confirming that unknown query parameters are ignored.
- Revised documentation to clarify the API's focus on duty shifts only, enhancing clarity for users.

duty_teller/api/app.py

@@ -3,8 +3,6 @@
 import logging
 import re
 from datetime import date, timedelta
-from typing import Literal
-
 import duty_teller.config as config
 from fastapi import Depends, FastAPI, Request
 from fastapi.middleware.cors import CORSMiddleware
@@ -100,20 +98,16 @@ def list_calendar_events(
     "/api/calendar/ical/{token}.ics",
     summary="Personal calendar ICS",
     description=(
-        "Returns an ICS calendar with the subscribing user's events. "
-        "By default only duty shifts are included; use query parameter events=all "
-        "for all event types (duty, unavailable, vacation). "
+        "Returns an ICS calendar with the subscribing user's duty shifts only. "
         "No Telegram auth; access is by secret token in the URL."
     ),
 )
 def get_personal_calendar_ical(
     token: str,
-    events: Literal["duty", "all"] = "duty",
     session: Session = Depends(get_db_session),
 ) -> Response:
     """
-    Return ICS calendar with the subscribing user's events.
-    Default: only duty shifts. Use ?events=all for duty, unavailable, vacation.
+    Return ICS calendar with the subscribing user's duty shifts only.
     No Telegram auth; access is by secret token in the URL.
     """
     if not _is_valid_calendar_token(token):
@@ -124,9 +118,8 @@ def get_personal_calendar_ical(
     today = date.today()
     from_date = (today - timedelta(days=365)).strftime("%Y-%m-%d")
     to_date = (today + timedelta(days=365 * 2)).strftime("%Y-%m-%d")
-    event_types = ["duty"] if events == "duty" else None
     duties_with_name = get_duties_for_user(
-        session, user.id, from_date=from_date, to_date=to_date, event_types=event_types
+        session, user.id, from_date=from_date, to_date=to_date, event_types=["duty"]
     )
     ics_bytes = build_personal_ics(duties_with_name)
     return Response(