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/package.json

@@ -13,7 +13,8 @@
     "lucide-react": "^0.553.0",
     "react": "^19.2.0",
     "react-dom": "^19.2.0",
-    "react-router-dom": "^7.9.5"
+    "react-router-dom": "^7.9.5",
+    "socket.io-client": "^4.8.1"
   },
   "devDependencies": {
     "@eslint/js": "^9.39.1",