feat(dashboard): add unread count for match chats

Track unread messages in match chats and display count badge:
- Schema: Add user1LastReadAt/user2LastReadAt to Match model
- Backend: Calculate unreadCount in dashboard API
- Socket: Update lastReadAt when user joins match room
- Frontend: Display red badge with unread count on match avatar

backend/src/routes/dashboard.js

@@ -180,6 +180,14 @@ router.get('/', authenticate, async (req, res, next) => {
       const lastMessage = match.room?.messages[0];
       const lastMessageAt = lastMessage ? lastMessage.createdAt : match.createdAt;
 
+      // Calculate unread count
+      const myLastReadAt = isUser1 ? match.user1LastReadAt : match.user2LastReadAt;
+      const unreadCount = myLastReadAt
+        ? (match.room?.messages || []).filter(
+            (m) => m.userId !== userId && new Date(m.createdAt) > new Date(myLastReadAt)
+          ).length
+        : (match.room?.messages || []).filter((m) => m.userId !== userId).length;
+
       return {
         id: match.id,
         slug: match.slug,
@@ -197,6 +205,7 @@ router.get('/', authenticate, async (req, res, next) => {
         },
         videoExchange,
         ratings,
+        unreadCount,
         lastMessageAt,
         status: match.status,
       };