Add calendar export, SEO, error monitoring, backups, audit trail, and a starter test suite

Six site improvements picked from a "what could be better" review, plus a Jest
test suite covering the two areas with the trickiest money-handling history
in this project (early-bird pricing tranches, donation-leg accounting):

- "Add to calendar" .ics download on event pages and in confirmation emails
- sitemap.xml, robots.txt, and Open Graph/Twitter metadata for public pages
- Sentry error monitoring (backend + frontend), a no-op until SENTRY_DSN is set
- Nightly local pg_dump backups with a Site Settings tab to browse/trigger/download
- Admin audit trail for refunds, donations, manual registrations, event and
  settings changes, and staff-initiated cancellations
- Jest tests reproducing and guarding against the 1.8.0 tranche-pricing bug
  and the 1.4.2 donation-balance-inflation bug

Wallet passes (Google/Apple) were scoped out of this round — Apple Wallet
needs a paid Apple Developer account the project doesn't have yet, and the
user preferred shipping both together later rather than Google alone now.

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

backend/src/index.js

@@ -11,6 +11,20 @@ const getRawBody = require('raw-body');
 // Load environment variables
 dotenv.config();
 
+// Error monitoring — a no-op if SENTRY_DSN isn't set, so this is safe in every
+// environment (dev, a fresh deploy that hasn't configured Sentry yet, etc.).
+// Must run before the Express app is created so its instrumentation can hook in.
+if (process.env.SENTRY_DSN) {
+  const Sentry = require('@sentry/node');
+  Sentry.init({
+    dsn: process.env.SENTRY_DSN,
+    environment: process.env.NODE_ENV || 'development',
+    // Small single-VM deployment, not high-traffic — start conservative and raise
+    // this once real usage is visible in Sentry, rather than sampling every request.
+    tracesSampleRate: 0.1,
+  });
+}
+
 // Initialize Prisma client
 const prisma = new PrismaClient();
 
@@ -126,6 +140,8 @@ const setupRoutes     = require('./routes/setupRoutes');
 const costRoutes      = require('./routes/costRoutes');
 const cashupRoutes    = require('./routes/cashupRoutes');
 const statsRoutes     = require('./routes/statsRoutes');
+const adminRoutes     = require('./routes/adminRoutes');
+const backupRoutes    = require('./routes/backupRoutes');
 
 // Mount webhook routes BEFORE JSON body parser to avoid double-reading the stream
 app.use('/api/webhooks', webhookRoutes);
@@ -155,6 +171,8 @@ app.use('/api/setup',    setupRoutes);
 app.use('/api/stats',    statsRoutes);
 app.use('/api', costRoutes);
 app.use('/api/cashups', cashupRoutes);
+app.use('/api/admin', adminRoutes);
+app.use('/api/backups', backupRoutes);
 
 // Pre-warm the settings cache so synchronous helpers have DB values from startup
 const { getSettingSync, warmCache } = require('./utils/settingsCache');
@@ -1134,6 +1152,14 @@ function toggle(id) {
 
 // Error middleware
 app.use(notFound);
+
+// Sentry captures the error here, then passes it through unchanged — errorHandler
+// below remains the sole source of what's actually sent back to the client.
+if (process.env.SENTRY_DSN) {
+  const Sentry = require('@sentry/node');
+  Sentry.setupExpressErrorHandler(app);
+}
+
 app.use(errorHandler);
 
 // Start server
@@ -1224,6 +1250,36 @@ app.listen(PORT, () => {
     console.warn('[temp cleanup] Not scheduled:', e?.message || e);
   }
 
+  // Nightly database backup at 02:00 local time (before the 03:00 temp cleanup)
+  try {
+    const enabled = String(process.env.BACKUP_ENABLED || 'true').toLowerCase() !== 'false';
+    if (enabled) {
+      const { runBackup } = require('./utils/backupUtils');
+      function scheduleNightlyBackup() {
+        const now = new Date();
+        const next = new Date(now);
+        next.setHours(2, 0, 0, 0);
+        if (next <= now) next.setDate(next.getDate() + 1);
+        setTimeout(async () => {
+          try {
+            const result = await runBackup();
+            console.log(`[backup] Completed: ${result.filename}`);
+          } catch (e) {
+            console.error('[backup] Failed:', e?.message || e);
+          } finally {
+            scheduleNightlyBackup();
+          }
+        }, next.getTime() - now.getTime());
+      }
+      scheduleNightlyBackup();
+      console.log('[backup] Scheduler initialized (02:00 local time). Set BACKUP_ENABLED=false to disable.');
+    } else {
+      console.log('[backup] Scheduler disabled by env BACKUP_ENABLED=false');
+    }
+  } catch (e) {
+    console.warn('[backup] Not scheduled:', e?.message || e);
+  }
+
   // Scheduled emails worker (polling)
   try {
     const enabled = String(process.env.SCHEDULED_EMAILS_ENABLED || 'true').toLowerCase() !== 'false';
@@ -1287,6 +1343,9 @@ app.listen(PORT, () => {
 process.on('unhandledRejection', (err) => {
   console.error('UNHANDLED REJECTION!', err?.name, err?.message);
   console.error(err?.stack || err);
+  if (process.env.SENTRY_DSN) {
+    try { require('@sentry/node').captureException(err); } catch {}
+  }
 });
 
 module.exports = { app, prisma };