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

frontend/src/pages/DashboardPage.jsx

@@ -326,6 +326,12 @@ const EventCard = ({ event }) => {
         <div className="flex items-center gap-2">
           <Users className="w-4 h-4 flex-shrink-0" />
           <span>{event.participantsCount} participants</span>
+          {event.onlineCount > 0 && (
+            <span className="text-green-600 flex items-center gap-1">
+              <span className="w-2 h-2 bg-green-500 rounded-full animate-pulse" />
+              {event.onlineCount} online
+            </span>
+          )}
         </div>
       </div>
 

frontend/src/pages/__tests__/DashboardPage.test.jsx

@@ -128,6 +128,59 @@ describe('DashboardPage', () => {
       });
     });
 
+    it('should display online count when users are online', async () => {
+      dashboardAPI.getData.mockResolvedValue({
+        activeEvents: [
+          {
+            id: 1,
+            slug: 'test-event',
+            name: 'Test Event',
+            location: 'Warsaw',
+            startDate: '2025-12-01',
+            endDate: '2025-12-03',
+            participantsCount: 50,
+            onlineCount: 5,
+            myHeats: [],
+          },
+        ],
+        activeMatches: [],
+        matchRequests: { incoming: [], outgoing: [] },
+      });
+
+      renderWithRouter(<DashboardPage />);
+
+      await waitFor(() => {
+        expect(screen.getByText('5 online')).toBeInTheDocument();
+      });
+    });
+
+    it('should not display online count when zero', async () => {
+      dashboardAPI.getData.mockResolvedValue({
+        activeEvents: [
+          {
+            id: 1,
+            slug: 'test-event',
+            name: 'Test Event',
+            location: 'Warsaw',
+            startDate: '2025-12-01',
+            endDate: '2025-12-03',
+            participantsCount: 50,
+            onlineCount: 0,
+            myHeats: [],
+          },
+        ],
+        activeMatches: [],
+        matchRequests: { incoming: [], outgoing: [] },
+      });
+
+      renderWithRouter(<DashboardPage />);
+
+      await waitFor(() => {
+        expect(screen.getByText('Test Event')).toBeInTheDocument();
+      });
+      expect(screen.queryByText(/online/)).not.toBeInTheDocument();
+    });
+
     it('should navigate to event chat when clicking Enter Chat', async () => {
       dashboardAPI.getData.mockResolvedValue({
         activeEvents: [