feat: implement real-time chat with Socket.IO

Implemented WebSocket-based real-time messaging for both event rooms and private match chats using Socket.IO with comprehensive test coverage.

Backend changes:
- Installed socket.io@4.8.1 for WebSocket server
- Created Socket.IO server with JWT authentication middleware
- Implemented event room management (join/leave/messages)
- Added active users tracking with real-time updates
- Implemented private match room messaging
- Integrated Socket.IO with Express HTTP server
- Messages are persisted to PostgreSQL via Prisma
- Added 12 comprehensive unit tests (89.13% coverage)

Frontend changes:
- Installed socket.io-client for WebSocket connections
- Created socket service layer for connection management
- Updated EventChatPage with real-time messaging
- Updated MatchChatPage with real-time private chat
- Added connection status indicators (● Connected/Disconnected)
- Disabled message input when not connected

Infrastructure:
- Updated nginx config to proxy WebSocket connections at /socket.io
- Added Upgrade and Connection headers for WebSocket support
- Set long timeouts (7d) for persistent WebSocket connections

Key features:
- JWT-authenticated socket connections
- Room-based architecture for events and matches
- Real-time message broadcasting
- Active users list with automatic updates
- Automatic cleanup on disconnect
- Message persistence in database

Test coverage:
- 12 tests passing (authentication, event rooms, match rooms, disconnect, errors)
- Socket.IO module: 89.13% statements, 81.81% branches, 91.66% functions
- Overall coverage: 81.19%

Phase 1, Step 4 completed. Ready for Phase 2 (Core Features).

frontend/src/services/socket.js

@@ -0,0 +1,56 @@
+import { io } from 'socket.io-client';
+
+const SOCKET_URL = 'http://localhost:8080';
+
+let socket = null;
+
+export function connectSocket() {
+  const token = localStorage.getItem('token');
+
+  if (!token) {
+    console.error('No token found for socket connection');
+    return null;
+  }
+
+  if (socket && socket.connected) {
+    return socket;
+  }
+
+  socket = io(SOCKET_URL, {
+    auth: {
+      token,
+    },
+    reconnection: true,
+    reconnectionAttempts: 5,
+    reconnectionDelay: 1000,
+  });
+
+  socket.on('connect', () => {
+    console.log('✅ Socket connected:', socket.id);
+  });
+
+  socket.on('disconnect', (reason) => {
+    console.log('❌ Socket disconnected:', reason);
+  });
+
+  socket.on('connect_error', (error) => {
+    console.error('Socket connection error:', error.message);
+  });
+
+  socket.on('error', (error) => {
+    console.error('Socket error:', error);
+  });
+
+  return socket;
+}
+
+export function disconnectSocket() {
+  if (socket) {
+    socket.disconnect();
+    socket = null;
+  }
+}
+
+export function getSocket() {
+  return socket;
+}