Lets staff redeem a registration's Main Tickets by quantity at the door
(via the Payment/registration flow) instead of scanning each QR code,
and automatically emails/WhatsApps a check-in confirmation to the
attendee. Also routes the At The Door "Open" button and post-payment
flow dynamically: paid registrations jump straight to Check-In instead
of a forced ticket print, since tickets are already sent automatically.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>