Fix ready button state after game over

- Enable ready button in resetLobbyState() so players can ready up
- Remove redundant ready button state reset from endGame()
- Ensure ready button is enabled when returning to lobby

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

public/js/app.js

@@ -229,10 +229,6 @@ function endGame(states) {
   network.isSpectator = false;
   ui.hideSpectatorMode();
 
-  // Reset ready button state
-  ui.buttons.ready.textContent = 'READY';
-  ui.buttons.ready.disabled = true;
-
   ui.showGameOver(winner, scores);
 }