refactor: delegate signal effects to DisposableBag

Introduce `addEffect` to `DisposableBag` to encapsulate Preact
signal effect creation and disposal. Update `ReactiveScene` to use
this method, simplifying effect management and ensuring proper
cleanup.

packages/framework/src/utils/disposable.ts

@@ -1,3 +1,5 @@
+import { effect } from "@preact/signals-core";
+
 export interface IDisposable {
   dispose(): void;
 }
@@ -8,6 +10,10 @@ export class DisposableBag implements IDisposable {
   private _disposables = new Set<DisposableItem>();
   private _isDisposed = false;
 
+  constructor(go?: Phaser.GameObjects.GameObject) {
+    if (go) go.on("shutdown", () => this.dispose());
+  }
+
   get isDisposed(): boolean {
     return this._isDisposed;
   }
@@ -20,6 +26,10 @@ export class DisposableBag implements IDisposable {
     this._disposables.add(item);
   }
 
+  addEffect(fn: () => void) {
+    this.add(effect(fn));
+  }
+
   dispose(): void {
     if (this._isDisposed) return;