fix: improve doc link navigation and tree display

- Fix link resolution with proper relative/absolute path handling
- Improve link styling with underline decoration
- Hide leaf nodes from tree, only show directories
- Fix log file path for packaged app

docs/api/math/h/pi.md

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+# Math::PI
+
+```cpp
+constexpr float PI = 3.14159265358979323846f;
+```
+
+圆周率常量，精确到 float 能表示的最高精度。
+
+**用途：** 用于三角函数计算、弧度角度转换、圆形/弧度相关计算。
+
+**示例：**
+
+```cpp
+#include <XCEngine/Math/Math.h>
+
+float circumference = 2.0f * Math::PI * radius;
+float area = Math::PI * radius * radius;
+```
+
+## 相关文档
+
+- [Math 总览](h.md) - 返回 Math 概览