Fix inventory disappearing: add WS keep-alive pings + HTTP API fallback

- Server pings web clients every 25s to keep connections alive through reverse proxies
- Client fetches /api/inventory on page load (doesn't depend solely on WebSocket)
- Prevent duplicate WebSocket connections on reconnect
- Deduplicate initial_state/state_update handlers

web/server/server.js

@@ -469,6 +469,7 @@ wss.on('connection', (ws, req) => {
   // ---- Web client WebSocket connection ----
   console.log('🌐 New web client connected');
   webClients.add(ws);
+  ws.isAlive = true;
   
   // Send current state to new client
   ws.send(JSON.stringify({
@@ -484,10 +485,11 @@ wss.on('connection', (ws, req) => {
     lastUpdate,
   }));
   
+  ws.on('pong', () => { ws.isAlive = true; });
+  
   ws.on('message', (message) => {
     try {
       const data = JSON.parse(message);
-      console.log('📨 Received from web client:', data);
       
       if (data.type === 'command') {
         // Forward command to bridge
@@ -508,6 +510,23 @@ wss.on('connection', (ws, req) => {
   });
 });
 
+// ========== WebSocket Keep-Alive ==========
+// Ping all web clients every 25s to keep connections alive through reverse proxies
+const WS_PING_INTERVAL = setInterval(() => {
+  webClients.forEach((ws) => {
+    if (!ws.isAlive) {
+      webClients.delete(ws);
+      return ws.terminate();
+    }
+    ws.isAlive = false;
+    ws.ping();
+  });
+}, 25000);
+
+wss.on('close', () => {
+  clearInterval(WS_PING_INTERVAL);
+});
+
 // ========== Start Server ==========
 
 server.listen(PORT, HOST, () => {