- add "Geburtstagskalender" to the sidebar +calendar dropdown and a "+ Geburtstage"
button to Settings > Calendars; both call ensureBirthdayCalendar (server enforces
one per account) and toast "already exists" if present
- Settings birthday section: when none exists, just a hint pointing to "+ Geburtstage"
(creation lives in the add area now, not a separate activate button)
- resizable calendar table: sensible default column widths instead of raw measured
- i18n de/en
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>