feat(notifications): add unified multi-channel notification system

Introduces a fully featured notification system with three delivery
channels (in-app, email, webhook), normalized per-user/per-event/
per-channel preferences, admin-scoped notifications, scheduled trip
reminders and version update alerts.

- New notificationService.send() as the single orchestration entry point
- In-app notifications with simple/boolean/navigate types and WebSocket push
- Per-user preference matrix with normalized notification_channel_preferences table
- Admin notification preferences stored globally in app_settings
- Migration 69 normalizes legacy notification_preferences table
- Scheduler hooks for daily trip reminders and version checks
- DevNotificationsPanel for testing in dev mode
- All new tests passing, covering dispatch, preferences, migration, boolean
  responses, resilience, and full API integration (NSVC, NPREF, INOTIF,
  MIGR, VNOTIF, NROUTE series)
 - Previous tests passing

server/src/routes/packing.ts

@@ -224,13 +224,10 @@ router.put('/category-assignees/:categoryName', authenticate, (req: Request, res
 
   // Notify newly assigned users
   if (Array.isArray(user_ids) && user_ids.length > 0) {
-    import('../services/notifications').then(({ notify }) => {
+    import('../services/notificationService').then(({ send }) => {
       const tripInfo = db.prepare('SELECT title FROM trips WHERE id = ?').get(tripId) as { title: string } | undefined;
-      for (const uid of user_ids) {
-        if (uid !== authReq.user.id) {
-          notify({ userId: uid, event: 'packing_tagged', params: { trip: tripInfo?.title || 'Untitled', actor: authReq.user.email, category: cat } }).catch(() => {});
-        }
-      }
+      // Use trip scope so the service resolves recipients — actor is excluded automatically
+      send({ event: 'packing_tagged', actorId: authReq.user.id, scope: 'trip', targetId: Number(tripId), params: { trip: tripInfo?.title || 'Untitled', actor: authReq.user.email, category: cat, tripId: String(tripId) } }).catch(() => {});
     });
   }
 });