Fixed
- Fix all-day calendar events appearing on the correct day and the following day — ICS DTEND for DATE values is exclusive per RFC 5545, now correctly adjusted (fixes #5)
- Fix multi-day events not showing when using DURATION instead of DTEND — add ICS DURATION property support in CalDAV parser
- Fix birthdays from Apple Calendar not syncing — birthday calendars are no longer excluded from sync
- Fix outbound ICS builder using inclusive DTEND for all-day events — now correctly emits exclusive DTEND per RFC 5545