feat: interactive AskUserQuestion + WebSocket stability

- Add WebSocket heartbeat (30s ping/pong) to prevent proxy timeouts
- Add auto-reconnect with exponential backoff (1s-30s, max 10 attempts)
- Add interactive AskUserQuestion rendering with clickable options
- Add custom input field for free-text answers
- Add smooth animations (hover, selection glow, checkbox scale)
- Make interactive tool cards wider (max-w-2xl) without scrolling
- Hide error badge and result section for interactive tools
- Use TextareaAutosize for lag-free custom input
- Add Skill, SlashCommand tool renderings
- Add ThinkingBlock component for collapsible <thinking> tags

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/server.js

@@ -129,6 +129,9 @@ function generateRequestId() {
 const server = createServer(app);
 const wss = new WebSocketServer({ server });
 
+// WebSocket heartbeat interval (30 seconds)
+const WS_HEARTBEAT_INTERVAL = 30000;
+
 // Scan directory for projects
 function scanProjects(basePath, depth = 0, maxDepth = 1) {
   const projects = [];
@@ -560,6 +563,20 @@ wss.on('connection', async (ws, req) => {
   const sessionId = uuidv4();
   console.log(`[${sessionId}] New WebSocket connection`);
 
+  // Track connection health
+  ws.isAlive = true;
+
+  // Heartbeat to keep connection alive through proxies
+  const heartbeatInterval = setInterval(() => {
+    if (ws.readyState === ws.OPEN) {
+      ws.ping();
+    }
+  }, WS_HEARTBEAT_INTERVAL);
+
+  ws.on('pong', () => {
+    ws.isAlive = true;
+  });
+
   // Authenticate WebSocket connection
   let wsUser = null;
   if (authConfig.app.authEnabled && sessionStore) {
@@ -1030,6 +1047,8 @@ wss.on('connection', async (ws, req) => {
 
   ws.on('close', () => {
     console.log(`[${sessionId}] WebSocket closed`);
+    clearInterval(heartbeatInterval);
+    clearInterval(cleanupInterval);
     if (claudeProcess) {
       claudeProcess.kill();
       sessions.delete(sessionId);