feat: add class discounts, frontend visibility, and public listing

Add hasDiscount, freeSpots, and showOnFrontend on classes with a public get-all endpoint and richer notification user populate.

components/notifications/notificationService.js

@@ -49,7 +49,7 @@ const getAllNotifications = async (queryParams) => {
   const filter = buildFilterQuery(queryParams, ['subject', 'body']);
 
   const [notifications, totalCount] = await Promise.all([
-    Notification.find(filter).populate('user', 'name username').sort(sort).skip(skip).limit(limit),
+    Notification.find(filter).populate('user', 'name username phoneNumber').sort(sort).skip(skip).limit(limit),
     Notification.countDocuments(filter)
   ]);