CreateEventTool
Inserts a new event into CalendarContract.Events via ContentResolver. Requires WRITE_CALENDAR. start/end are parsed as yyyy-MM-dd HH:mm (device timezone); when calendar_id is omitted it falls back to the primary calendar (or first available, see getPrimaryCalendarId). Output: event_id (the inserted row id, may be null if the URI lacks a numeric segment), plus echoed title, start, and end.