feat: enforce playlist selection before starting the game and update playlist handling

public/js/ui.js

@@ -121,7 +121,14 @@ export function wireUi() {
     $room.classList.add('hidden');
   });
 
-  wire($startGame, 'click', () => sendMsg({ type: 'start_game' }));
+  wire($startGame, 'click', () => {
+    // Validate playlist selection before starting
+    if (!state.room?.state?.playlist) {
+      showToast('⚠️ Bitte wähle zuerst eine Playlist aus!');
+      return;
+    }
+    sendMsg({ type: 'start_game' });
+  });
 
   wire($readyChk, 'change', (e) => {
     const val = !!e.target.checked;