Websockets instead of polling

frontend/src/pages/Dashboard.svelte

@@ -18,6 +18,10 @@
     let state = null;
     let error = '';
     let intervalId;
+    let ws = null;
+    let reconnectTimer = null;
+    let reconnectDelay = 1000;
+    let destroyed = false;
 
     async function fetchState() {
         try {
@@ -29,10 +33,28 @@
         }
     }
 
+    // The server pushes a ping over this socket whenever the game changes;
+    // each ping triggers a refetch of the state blob.
+    function connectSocket() {
+        const proto = location.protocol === 'https:' ? 'wss' : 'ws';
+        ws = new WebSocket(`${proto}://${location.host}/api/game/${gameId}/ws`);
+        ws.onopen = () => {
+            reconnectDelay = 1000;
+            fetchState(); // catch up on anything missed while disconnected
+        };
+        ws.onmessage = () => fetchState();
+        ws.onclose = () => {
+            if (destroyed) return;
+            reconnectTimer = setTimeout(connectSocket, reconnectDelay);
+            reconnectDelay = Math.min(reconnectDelay * 2, 10000);
+        };
+    }
+
     onMount(() => {
         fetchState();
-        // Poll every 2 seconds
-        intervalId = setInterval(fetchState, 2000);
+        connectSocket();
+        // Slow fallback poll in case a push is ever missed
+        intervalId = setInterval(fetchState, 30000);
     });
 
     // Surface the creator-only Admin link in the corner menu
@@ -43,7 +65,10 @@
     );
 
     onDestroy(() => {
+        destroyed = true;
         if (intervalId) clearInterval(intervalId);
+        if (reconnectTimer) clearTimeout(reconnectTimer);
+        if (ws) ws.close();
         extraMenuLinks.set([]);
     });
 </script>