Engine: 实现 Components 和 Scene 模块，包含完整单元测试

新增 Components 模块:
- Component 基类 (生命周期、启用状态管理)
- TransformComponent (本地/世界空间变换、矩阵缓存、父子层级)
- GameObject (组件管理、父子层级、激活状态、静态查找)

新增 Scene 模块:
- Scene (场景管理、对象创建销毁、查找、生命周期)
- SceneManager (单例模式、多场景管理、场景切换)

新增测试:
- test_component.cpp (12 个测试)
- test_transform_component.cpp (35 个测试)
- test_game_object.cpp (26 个测试)
- test_scene.cpp (20 个测试)
- test_scene_manager.cpp (17 个测试)

所有测试均已编译通过。

tests/Scene/CMakeLists.txt

@@ -0,0 +1,28 @@
+cmake_minimum_required(VERSION 3.15)
+
+project(XCEngine_SceneTests)
+
+set(SCENE_TEST_SOURCES
+    test_scene.cpp
+    test_scene_manager.cpp
+)
+
+add_executable(xcengine_scene_tests ${SCENE_TEST_SOURCES})
+
+if(MSVC)
+    set_target_properties(xcengine_scene_tests PROPERTIES
+        LINK_FLAGS "/NODEFAULTLIB:libcpmt.lib /NODEFAULTLIB:libcmt.lib"
+    )
+endif()
+
+target_link_libraries(xcengine_scene_tests PRIVATE
+    XCEngine
+    GTest::gtest
+    GTest::gtest_main
+)
+
+target_include_directories(xcengine_scene_tests PRIVATE
+    ${CMAKE_SOURCE_DIR}/engine/include
+)
+
+add_test(NAME SceneTests COMMAND xcengine_scene_tests)