docs: Add Component, GameObject, TransformComponent and Scene API documentation

- Add Component class documentation with lifecycle methods
- Add GameObject class documentation with component system
- Add TransformComponent documentation with transform methods
- Add Scene class documentation with GameObject management
- Add SceneManager singleton documentation with scene loading
- Update components.md overview with all component classes
- Update main.md navigation with Scene module

docs/api/components/game-object/start.md

@@ -0,0 +1,15 @@
+# GameObject::Start
+
+开始游戏对象及其所有组件。
+
+```cpp
+void Start();
+```
+
+在首次 Update 之前调用，用于在游戏逻辑开始前完成初始化。
+
+## 相关文档
+
+- [GameObject 总览](game-object.md)
+- [Awake](awake.md)
+- [Update](update.md)