feat(backup): full DR bundle export + admin-configurable offsite destinations

Backend-agnostic disaster-recovery backup engine that runs on the current
storage backend (no storage cutover required):

- Full-bundle export: db.dump (pg_dump custom) + every storage blob +
  manifest.json with per-object SHA-256, streamed as a tar. Entry points:
  admin UI download, GET /api/v1/admin/backup/export, scripts/create-full-backup.ts.
- Admin-configurable push destinations (backup_destinations table, migration
  0091): SFTP/SSH, S3-compatible (reuses the minio client), and mounted
  path/NAS behind one transport interface (test/push/prune). Secrets AES-GCM
  at rest; API returns only *IsSet markers.
- Opt-in per-destination AES-256 bundle encryption (scrypt KDF, streamed) +
  scripts/decrypt-backup.ts for restore.
- Wired the previously-dead database-backup cron to runScheduledBackupPush
  (push to enabled destinations, prune to retention, alert super-admins on
  failure).

Tests: 1608 unit/integration pass; tsc + lint clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/lib/queue/workers/maintenance.ts

@@ -38,6 +38,17 @@ export const maintenanceWorker = new Worker(
         await refreshRates();
         break;
       }
+      case 'database-backup': {
+        // Scheduled full-bundle backup pushed to every enabled destination.
+        // No-op until an admin turns the schedule on AND enables a destination
+        // (`backup_schedule` setting + `backup_destinations`). Replaces the
+        // previous silent no-op (this case did not exist before).
+        const { runScheduledBackupPush } =
+          await import('@/lib/services/backup-destinations.service');
+        const summary = await runScheduledBackupPush();
+        logger.info(summary, 'Scheduled backup push complete');
+        break;
+      }
       case 'form-expiry-check': {
         const result = await db
           .update(formSubmissions)