Fixed
- The CalDAV calendar selected under "Sync to CalDAV" when creating or editing an event is now persisted (#241). The create and update endpoints previously dropped
target_caldav_account_idandtarget_caldav_calendar_url, so the selection reset to "Local" after saving and the event was never synced to the CalDAV server. Invalid account IDs are now rejected with a 400 instead of being silently ignored.