fix(05-jamtrack): get subscribe/unsubscribe methods from context correctly

Issue: "WebSocket connection not available" error
Root cause: Getting 'server' object instead of subscribe/unsubscribe methods

Fix: Extract subscribe/unsubscribe directly from useJamServerContext()
and create jamServer object with those methods for the thunks.

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

jam-ui/src/components/client/JKSessionJamTrackPlayer.js

@@ -38,7 +38,13 @@ const JKSessionJamTrackPlayer = ({
   const [selectedMixdownId, setSelectedMixdownId] = useState(initialMixdownId);
 
   // Context
-  const { server: jamServer } = useJamServerContext();
+  const { subscribe, unsubscribe } = useJamServerContext();
+
+  // Create jamServer object with subscribe/unsubscribe for thunks
+  const jamServer = useMemo(() => ({
+    subscribe,
+    unsubscribe
+  }), [subscribe, unsubscribe]);
 
   // Redux state
   const dispatch = useDispatch();