fix: add missing RPC methods and WebSocket heartbeat to mock backend

- Add node-messages-received, node.messages, node.notifications stubs
- Send WebSocket heartbeat every 45s to prevent client disconnect at 60s

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

neode-ui/mock-backend.js

@@ -893,7 +893,14 @@ app.post('/rpc/v1', (req, res) => {
         return res.json({ result: { success: true } })
       }
 
+      case 'node-messages-received':
+      case 'node.messages':
+      case 'node.notifications': {
+        return res.json({ result: [] })
+      }
+
       default: {
+        console.log(`[RPC] Unknown method: ${method}`)
         return res.json({
           error: {
             code: -32601,
@@ -934,12 +941,23 @@ wss.on('connection', (ws, req) => {
       } catch (err) {
         console.error('[WebSocket] Ping error:', err)
         clearInterval(pingInterval)
+        clearInterval(heartbeatInterval)
       }
     } else {
       clearInterval(pingInterval)
+      clearInterval(heartbeatInterval)
     }
   }, 30000) // Ping every 30 seconds
 
+  // Send periodic heartbeat data so clients don't think the connection is dead
+  const heartbeatInterval = setInterval(() => {
+    if (ws.readyState === 1) {
+      try {
+        ws.send(JSON.stringify({ rev: Date.now(), patch: [] }))
+      } catch { /* ignore */ }
+    }
+  }, 45000) // Every 45s (client expects data within 60s)
+
   // Send initial data immediately
   try {
     ws.send(JSON.stringify({
@@ -968,12 +986,14 @@ wss.on('connection', (ws, req) => {
   ws.on('close', (code, reason) => {
     console.log('[WebSocket] Client disconnected', { code, reason: reason.toString() })
     clearInterval(pingInterval)
+    clearInterval(heartbeatInterval)
     wsClients.delete(ws)
   })
 
   ws.on('error', (error) => {
     console.error('[WebSocket Error]', error)
     clearInterval(pingInterval)
+    clearInterval(heartbeatInterval)
     wsClients.delete(ws)
   })
 })