feat(dashboard): add online count for events

Show real-time count of users currently in each event chat room.
- Backend: Export getEventsOnlineCounts from socket module
- Dashboard API: Include onlineCount for each active event
- Frontend: Display online count with animated green dot indicator

backend/src/routes/dashboard.js

@@ -7,6 +7,7 @@ const express = require('express');
 const router = express.Router();
 const { authenticate } = require('../middleware/auth');
 const { PrismaClient } = require('@prisma/client');
+const { getEventsOnlineCounts } = require('../socket');
 
 const prisma = new PrismaClient();
 
@@ -38,6 +39,15 @@ router.get('/', authenticate, async (req, res, next) => {
       },
     });
 
+    // Get online counts for all events (safely handle if socket not initialized)
+    let onlineCounts = {};
+    try {
+      const eventIds = eventParticipants.map(ep => ep.event.id);
+      onlineCounts = getEventsOnlineCounts(eventIds);
+    } catch (_) {
+      // Socket may not be initialized (e.g., during tests)
+    }
+
     // Get user's heats for each event
     const activeEvents = await Promise.all(
       eventParticipants.map(async (ep) => {
@@ -72,6 +82,7 @@ router.get('/', authenticate, async (req, res, next) => {
           startDate: ep.event.startDate,
           endDate: ep.event.endDate,
           participantsCount: ep.event.participantsCount,
+          onlineCount: onlineCounts[ep.event.id] || 0,
           myHeats: heats.map((h) => ({
             id: h.id,
             competitionType: h.competitionType,