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/index.js

@@ -1192,13 +1192,14 @@ app.listen(PORT, () => {
   try {
     const enabled = String(process.env.SCHEDULED_EMAILS_ENABLED || 'true').toLowerCase() !== 'false';
     if (enabled) {
-      const { getDueJobs, updateJob } = require('./utils/scheduledEmails');
+      const { getDueJobs, updateJob, purgeSentJobs } = require('./utils/scheduledEmails');
       const { emailEventAttendees, whatsappEventAttendees } = require('./controllers/eventController');
       const { sendBroadcast } = require('./controllers/broadcastController');
       const { sendWhatsAppBroadcast } = require('./controllers/whatsappBroadcastController');
       const intervalMs = parseInt(process.env.SCHEDULED_EMAILS_INTERVAL_MS || '30000', 10);
       setInterval(async () => {
         try {
+          try { purgeSentJobs(24 * 60 * 60 * 1000); } catch (e) { console.warn('[scheduled emails] purge failed:', e?.message || e); }
           const due = getDueJobs(new Date());
           if (!due || due.length === 0) return;
           for (const job of due) {