fix: wait for fade scene init

packages/framework/src/scenes/FadeScene.ts

@@ -57,6 +57,12 @@ export class FadeScene extends ReactiveScene<FadeSceneData> {
      * 淡入淡出到指定透明度
      */
     private fadeTo(targetAlpha: number, duration: number): Promise<void> {
+        // 如果 overlay 还未初始化，直接返回 resolved promise
+        if (!this.overlay) {
+            console.warn('FadeScene: overlay 未初始化，跳过过渡动画');
+            return Promise.resolve();
+        }
+
         if (this.isFading) {
             console.warn('FadeScene: 正在进行过渡动画');
         }