- Import computeNewTimedEnd/computeNewAllDayEnd from eventDateTime.ts (D-04)
- Start date onChange: calls computeNewAllDayEnd (all-day) or computeNewTimedEnd (timed)
- Start time onChange: calls computeNewTimedEnd preserving duration (timed only)
- Add recurrenceBound/recurrenceUntil/recurrenceCount state (D-06)
- Reset useEffect extended to reset bound state on form open
- Add 'Ends' control (Never/On date/After N times) shown when recurrence != none
- Inline validation: count < 1 and until < start
- Payload conditionally includes recurrenceUntil/recurrenceCount (create mode only)
- Error state type extended for recurrenceBound validation