Add unready toggle in lobby

- Server: Handle unready event to set player ready state to false
- Client: Ready button toggles between READY and UNREADY
- Client: Unready sends unready socket event to server

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

public/index.html

@@ -62,10 +62,10 @@
   </div>
 
   <script src="/socket.io/socket.io.js"></script>
-  <script src="js/network.js?v=5"></script>
+  <script src="js/network.js?v=6"></script>
   <script src="js/game.js?v=4"></script>
   <script src="js/renderer.js?v=5"></script>
-  <script src="js/ui.js?v=5"></script>
+  <script src="js/ui.js?v=6"></script>
   <script src="js/app.js?v=5"></script>
 </body>
 </html>