* Align EntityFrameworkCore.SqlServer and Tools to 8.0.8
* Add calendar/events backend API
Cherry-picked from main-backup (19994ef); scratch notes file removed.
* Require authentication on CalendarController
Security review found [Authorize] commented out, leaving all 6 calendar
endpoints anonymous. Enforce auth to match the API convention (17/23
controllers).
* Add CalendarController unit tests (xUnit + EF InMemory)
