feat(websocket): add ping/pong mechanism to maintain connection

- Add proxy timeouts in nginx.conf to handle long connections
- Implement ping/pong handling in server.js WebSocket listener
- Refactor App.js to class component with lifecycle methods and ping interval for WebSocket keep-alive

server.js

@@ -33,7 +33,13 @@ wss.on('connection', (ws) => {
   console.log('Client connected');
 
   ws.on('message', (message) => {
-    console.log('Received:', Buffer.from(message).toString());
+    const msg = Buffer.from(message).toString();
+    if (msg === '{"type":"ping"}') {
+      // Respond to ping to keep connection alive
+      ws.send(JSON.stringify({ type: 'pong' }));
+    } else {
+      console.log('Received:', msg);
+    }
   });
 
   ws.on('error', (error) => {