- BookingCalendar: remove type badge below room number (already shown in group header) - RoomModal: validate number against existingNumbers before save - Red border + error message if number taken - Placeholder shows next free number (e.g. if 101,102 exist → placeholder 103) - Save button disabled while number is taken Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>