docs: update math API docs

docs/api/math/bounds/getclosestpoint.md

@@ -4,17 +4,35 @@
 Vector3 GetClosestPoint(const Vector3& point) const
 ```
 
-获取包围盒上最接近给定点的点。
+获取包围盒上最接近给定点的点。如果点在盒内，则返回该点本身；如果在盒外，则返回该点在盒面上的投影点。
 
 **参数：**
 - `point` - 参考点
 
 **返回：** `Vector3` - 盒上最接近的点
 
+**线程安全：** ✅
+
 **复杂度：** O(1)
 
 **示例：**
 
 ```cpp
-Vector3 closest = bounds.GetClosestPoint(point);
+#include <XCEngine/Math/Bounds.h>
+#include <XCEngine/Math/Vector3.h>
+
+using namespace XCEngine::Math;
+
+Bounds bounds(Vector3(0.0f, 0.0f, 0.0f), Vector3(2.0f, 2.0f, 2.0f));
+
+Vector3 inside = bounds.GetClosestPoint(Vector3(0.0f, 0.0f, 0.0f));
+// returns (0, 0, 0) since point is inside
+
+Vector3 outside = bounds.GetClosestPoint(Vector3(10.0f, 0.0f, 0.0f));
+// returns (1, 0, 0) - closest point on box surface
 ```
+
+## 相关文档
+
+- [Bounds](bounds.md) - 返回类总览
+- [Contains](contains.md) - 检测点是否在盒内