Update API documentation and remove obsolete plan files

docs/api/math/viewport/getrect.md

@@ -1,34 +1,18 @@
 # Viewport::GetRect
 
 ```cpp
-Rect GetRect() const;
+Rect GetRect() const
 ```
 
 将视口转换为 Rect。
 
-**返回：** 对应的 Rect（x, y, width, height），不包含深度范围
-
-**线程安全：** ✅
+**返回：** `Rect` - 对应的矩形 (x, y, width, height)，不包含深度范围
 
 **复杂度：** O(1)
 
 **示例：**
 
 ```cpp
-#include "XCEngine/Math/Rect.h"
-#include <iostream>
-
-using namespace XCEngine::Math;
-
-int main() {
-    Viewport viewport(0.0f, 0.0f, 1920.0f, 1080.0f, 0.0f, 1.0f);
-    Rect rect = viewport.GetRect();
-    std::cout << "Rect: (" << rect.x << ", " << rect.y << ", " << rect.width << ", " << rect.height << ")\n";
-    return 0;
-}
+Viewport viewport(0, 0, 1920, 1080, 0.0f, 1.0f);
+Rect rect = viewport.GetRect();  // (0, 0, 1920, 1080)
 ```
-
-## 相关文档
-
-- [`Viewport::GetAspectRatio`](getaspectratio.md) - 获取宽高比
-- [Viewport 总览](viewport.md)