- Add POST /calendar/slots/{slot_id}/cancel for real slot cancellation
- Add POST /calendar/slots/virtual/{virtual_id}/cancel for virtual slot cancellation
- Virtual cancel materializes the slot first, then marks as Skipped
- Both endpoints enforce past-slot immutability guard
- Both endpoints detach from plan (set plan_id=NULL)
- Status set to SlotStatus.SKIPPED on cancel
- Add TimeSlotCancelResponse schema
- Import guard_cancel_real_slot and guard_cancel_virtual_slot
zhi
16bcd94027