fix: scene switchWorld unmounts current scene before switching

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

public/js/core/scene.js

@@ -100,7 +100,14 @@ function transitionTo(sceneId, params, prevId, isBack = false) {
   }
 
   renderScene({ id: sceneId, params }, isBack);
-  setTimeout(() => { isTransitioning = false; }, 300);
+
+  const sceneEl = container.querySelector('.scene');
+  if (sceneEl) {
+    sceneEl.addEventListener('animationend', () => { isTransitioning = false; }, { once: true });
+    setTimeout(() => { isTransitioning = false; }, 400);
+  } else {
+    isTransitioning = false;
+  }
 }
 
 function renderScene(entry, isBack = false) {