- Add GetDistinctEventDates, UpdateEventWorkType, UpdateEventTime,
DeleteEvent, GetEventByID store methods to calendar.go
- Replace all 5 raw h.DB.DB().Exec/Query calls with proper store methods
- Remove unused database/sql import from calendar.go
- Rewrite GetLastEvent to use QueryRow instead of Query+manual iteration
(fixing row-vs-rows naming issue; removing rows.Close boilerplate)
- Add errors import to store.go for errors.Is