Extract computeAvailableHours as shared core between GetAvailableHours and GetPreviewAvailableHours, eliminating ~320 lines of duplication. Add GetConflictingBookingsForExceptionHandler (POST) for holiday hours conflict detection with batch service loading, int-based time comparison, and ActiveBookingStatuses constant. Add RESERVATION:placeholder cleanup (24h TTL). Fix scan error propagation in all scheduling row iterations. Add rows.Err() checks.
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