fix: 修复场景反序列化时子实体丢失的问题

在场景反序列化过程中，子实体虽然保持了父子引用关系，
但未被添加到 Scene 的实体集合和查询系统中，导致查询时子实体"丢失"。

packages/core/tests/ECS/Serialization/ParentChildSerialization.test.ts

@@ -0,0 +1,117 @@
+/**
+ * 父子实体序列化和反序列化测试
+ *
+ * 测试场景序列化和反序列化时父子实体关系的正确性
+ */
+
+import { Scene } from '../../../src';
+
+describe('父子实体序列化测试', () => {
+  let scene: Scene;
+
+  beforeEach(() => {
+    scene = new Scene({ name: 'TestScene' });
+  });
+
+  afterEach(() => {
+    scene.end();
+  });
+
+  test('应该正确反序列化父子实体层次结构', () => {
+    // 创建父实体
+    const parent = scene.createEntity('parent');
+    parent.tag = 100;
+
+    // 创建2个子实体
+    const child1 = scene.createEntity('child1');
+    child1.tag = 200;
+    parent.addChild(child1);
+
+    const child2 = scene.createEntity('child2');
+    child2.tag = 200;
+    parent.addChild(child2);
+
+    // 创建1个顶层实体（对照组）
+    const topLevel = scene.createEntity('topLevel');
+    topLevel.tag = 200;
+
+    // 验证序列化前的状态
+    expect(scene.querySystem.queryAll().entities.length).toBe(4);
+    expect(scene.findEntitiesByTag(100).length).toBe(1);
+    expect(scene.findEntitiesByTag(200).length).toBe(3);
+
+    // 序列化
+    const serialized = scene.serialize({ format: 'json' });
+
+    // 创建新场景并反序列化
+    const scene2 = new Scene({ name: 'LoadTestScene' });
+    scene2.deserialize(serialized as string, {
+      strategy: 'replace',
+      preserveIds: true,
+    });
+
+    // 验证所有实体都被正确恢复
+    const allEntities = scene2.querySystem.queryAll().entities;
+    expect(allEntities.length).toBe(4);
+    expect(scene2.findEntitiesByTag(100).length).toBe(1);
+    expect(scene2.findEntitiesByTag(200).length).toBe(3);
+
+    // 验证父子关系正确恢复
+    const restoredParent = scene2.findEntity('parent');
+    expect(restoredParent).not.toBeNull();
+    expect(restoredParent!.children.length).toBe(2);
+
+    const restoredChild1 = scene2.findEntity('child1');
+    const restoredChild2 = scene2.findEntity('child2');
+    expect(restoredChild1).not.toBeNull();
+    expect(restoredChild2).not.toBeNull();
+    expect(restoredChild1!.parent).toBe(restoredParent);
+    expect(restoredChild2!.parent).toBe(restoredParent);
+
+    scene2.end();
+  });
+
+  test('应该正确反序列化多层级实体层次结构', () => {
+    // 创建多层级实体结构：grandparent -> parent -> child
+    const grandparent = scene.createEntity('grandparent');
+    grandparent.tag = 1;
+
+    const parent = scene.createEntity('parent');
+    parent.tag = 2;
+    grandparent.addChild(parent);
+
+    const child = scene.createEntity('child');
+    child.tag = 3;
+    parent.addChild(child);
+
+    expect(scene.querySystem.queryAll().entities.length).toBe(3);
+
+    // 序列化
+    const serialized = scene.serialize({ format: 'json' });
+
+    // 创建新场景并反序列化
+    const scene2 = new Scene({ name: 'LoadTestScene' });
+    scene2.deserialize(serialized as string, {
+      strategy: 'replace',
+      preserveIds: true,
+    });
+
+    // 验证多层级结构正确恢复
+    expect(scene2.querySystem.queryAll().entities.length).toBe(3);
+
+    const restoredGrandparent = scene2.findEntity('grandparent');
+    const restoredParent = scene2.findEntity('parent');
+    const restoredChild = scene2.findEntity('child');
+
+    expect(restoredGrandparent).not.toBeNull();
+    expect(restoredParent).not.toBeNull();
+    expect(restoredChild).not.toBeNull();
+
+    expect(restoredParent!.parent).toBe(restoredGrandparent);
+    expect(restoredChild!.parent).toBe(restoredParent);
+    expect(restoredGrandparent!.children.length).toBe(1);
+    expect(restoredParent!.children.length).toBe(1);
+
+    scene2.end();
+  });
+});