fix: register checkQTE once in constructor instead of per-scene

Previously goToScene added a new checkQTE closure to onTimeUpdate on
every scene transition, accumulating stale closures that re-triggered
old QTE. Now checkQTE is an arrow property registered once in the
constructor, reading this.currentScene directly — no closure, no stale
references, no guard condition needed.

engine/core/Engine.ts

@@ -27,6 +27,8 @@ export class Engine {
     this.stateManager = new StateManager()
     this.choiceSystem = new ChoiceSystem()
     this.qteSystem = new QTESystem()
+
+    this.videoManager.onTimeUpdate(this.checkQTE)
   }
 
   on(event: EngineEvent, handler: EventHandler) {
@@ -70,10 +72,6 @@ export class Engine {
       }
     })
 
-    this.videoManager.onTimeUpdate((time) => {
-      this.checkQTE(scene, time)
-    })
-
     if (this.isInitialScene) {
       this.isInitialScene = false
       this.videoManager.playInitial(scene.videoUrl, preloadUrls)
@@ -84,9 +82,9 @@ export class Engine {
     this.emit('sceneChange', scene)
   }
 
-  private checkQTE(scene: SceneNode, time: number) {
-    if (this.currentScene?.id !== scene.id) return
-    if (!scene.qte || this.qteTriggered) return
+  private checkQTE = (time: number) => {
+    const scene = this.currentScene
+    if (!scene?.qte || this.qteTriggered) return
     if (time >= scene.qte.triggerTime) {
       this.qteTriggered = true
       const qte = scene.qte