Add door check-in flow for Main Tickets

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>

backend/src/controllers/ticketController.js

@@ -321,6 +321,7 @@ const scanTicket = async (req, res) => {
         e.title              AS "eventTitle",
         eo.id                AS "eventOptionId",
         eo.name              AS "eventOptionName",
+        eo."isMainTicket"    AS "isMainTicket",
         COALESCE(
           json_agg(
             json_build_object(
@@ -352,7 +353,7 @@ const scanTicket = async (req, res) => {
       isUsed:   r.isUsed,
       eventId:  r.eventId,
       event:    { title: r.eventTitle },
-      registrationOption: { eventOption: { id: r.eventOptionId, name: r.eventOptionName } },
+      registrationOption: { eventOption: { id: r.eventOptionId, name: r.eventOptionName, isMainTicket: r.isMainTicket } },
       usages:   r.usages || []
     };
 
@@ -398,6 +399,14 @@ const scanTicket = async (req, res) => {
       })
     ]);
 
+    // Only Main Tickets trigger a check-in notification (add-on tickets scanned via
+    // the QR camera flow are unaffected)
+    if (ticket.registrationOption?.eventOption?.isMainTicket) {
+      require('../utils/notifications')
+        .sendCheckInEmails(ticket.id, qtyToRedeem, newTotalRedeemed, newRemaining)
+        .catch(e => console.error('Failed to send check-in notification:', e));
+    }
+
     res.json({
       message: `Ticket scanned successfully (${qtyToRedeem} of ${ticket.quantity || 1} redeemed${newRemaining > 0 ? `, ${newRemaining} remaining` : ''})`,
       ticketUsage,