fix: improve doc link navigation and tree display

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docs/api/math/sphere/sphere.md

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+# Sphere
+
+3D 球体结构体。
+
+**头文件：** `#include <XCEngine/Math/Sphere.h>`
+
+**命名空间：** `XCEngine::Math`
+
+## 结构体定义
+
+```cpp
+struct Sphere {
+    Vector3 center = Vector3::Zero();
+    float radius = 0.0f;
+};
+```
+
+## 构造函数
+
+- `Sphere()` - 默认构造
+- `Sphere(const Vector3& center, float radius)` - 从中心和半径构造
+
+## 实例方法
+
+| 方法 | 返回值 | 描述 |
+|------|--------|------|
+| [Contains(point)](contains.md) | `bool` | 点是否在球体内 |
+| [Intersects(other)](intersects.md) | `bool` | 与另一个球体相交 |
+
+## 相关文档
+
+- [Math 模块总览](../math.md) - 返回 Math 模块总览