Fix scheduled WhatsApp messages sending as email; add 24h cleanup and recipient display

The scheduled-job store never persisted the channel field, so the
send worker always fell through to its email branch regardless of
what was requested. Also purges sent jobs 24h after sending instead
of keeping them forever, and surfaces who each scheduled job will go
to in the admin "manage scheduled" lists (now correctly filtered per
channel too).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/src/controllers/eventController.js

@@ -1569,6 +1569,15 @@ const whatsappEventAttendees = async (req, res) => {
   }
 };
 
+// Human-readable summary of who an attendees-scoped send will go to, for the scheduled-jobs admin UI
+function describeAttendeeFilter(filter) {
+  if (Array.isArray(filter?.attendeeIds) && filter.attendeeIds.length > 0) {
+    return `${filter.attendeeIds.length} selected attendee${filter.attendeeIds.length === 1 ? '' : 's'}`;
+  }
+  const labels = { paid: 'Paid attendees', unpaid: 'Unpaid attendees', partial_paid: 'Partially paid attendees', cancelled: 'Cancelled registrations' };
+  return labels[filter?.status] || 'All attendees';
+}
+
 // @desc    Schedule email to attendees at a specific date/time
 // @route   POST /api/events/:id/email-attendees/schedule
 // @access  Private/Supervisor or Admin
@@ -1600,6 +1609,7 @@ const scheduleEmailEventAttendees = async (req, res) => {
       eventId,
       createdById: req.user?.id || null,
       scheduledAt: when.toISOString(),
+      recipientSummary: `${event.title} — ${describeAttendeeFilter(filter)}`,
       payload,
     });
 
@@ -1637,6 +1647,7 @@ const scheduleWhatsappEventAttendees = async (req, res) => {
       channel: 'whatsapp',
       createdById: req.user?.id || null,
       scheduledAt: when.toISOString(),
+      recipientSummary: `${event.title} — ${describeAttendeeFilter(filter)}`,
       payload,
     });