- New Calendar model and calendars table with system/default flags
- Alembic migration 006: creates calendars, seeds Personal+Birthdays, migrates existing events
- CalendarEvent model gains calendar_id FK and calendar_name/calendar_color properties
- Updated CalendarEventCreate/Response schemas to include calendar fields
- New /api/calendars CRUD router (blocks system calendar deletion/rename)
- Events router: selectinload on all queries, default-calendar assignment on POST, virtual birthday event generation from People with birthdays when Birthdays calendar is visible
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
