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/rect/union.md

@@ -0,0 +1,23 @@
+# Rect::Union
+
+```cpp
+static Rect Union(const Rect& a, const Rect& b)
+```
+
+计算包含两矩形的最小矩形。
+
+**参数：**
+- `a` - 第一个矩形
+- `b` - 第二个矩形
+
+**返回：** `Rect` - 包含两矩形的最小外接矩形
+
+**复杂度：** O(1)
+
+**示例：**
+
+```cpp
+Rect rectA(0.0f, 0.0f, 50.0f, 50.0f);
+Rect rectB(100.0f, 100.0f, 50.0f, 50.0f);
+Rect combined = Rect::Union(rectA, rectB);  // (0, 0, 150, 150)
+```