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/containers/string/cstr.md

@@ -0,0 +1,36 @@
+# String::CStr
+
+```cpp
+const char* CStr() const;
+```
+
+返回指向以 null 结尾的 C 字符串的指针。
+
+**参数：** 无
+
+**返回：** 指向内部字符数组的指针，以 null 结尾
+
+**复杂度：** O(1)
+
+**示例：**
+```cpp
+#include "XCEngine/Containers/String.h"
+#include <iostream>
+#include <cstring>
+
+int main() {
+    XCEngine::Containers::String s("Hello World");
+
+    const char* cstr = s.CStr();
+    std::cout << cstr << std::endl;  // 输出: Hello World
+
+    std::cout << "Length: " << std::strlen(cstr) << std::endl;  // 输出: Length: 11
+
+    return 0;
+}
+```
+
+## 相关文档
+
+- [String 总览](string.md) - 返回类总览
+- [Length](size.md) - 获取长度