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/core/filewriter/IsOpen.md

@@ -0,0 +1,43 @@
+# FileWriter::IsOpen
+
+```cpp
+bool IsOpen() const;
+```
+
+检查文件是否已打开。
+
+**描述**
+
+返回文件是否已成功打开并可用于写入。
+
+**返回：** `bool` - 文件是否已打开
+
+**复杂度：** O(1)
+
+**示例：**
+
+```cpp
+#include <XCEngine/Core/FileWriter.h>
+
+using namespace XCEngine::Core;
+
+FileWriter writer1;
+if (writer1.IsOpen()) {
+    // 不会执行
+    writer1.Write("test");
+}
+
+// 打开文件
+FileWriter writer2("output.txt");
+if (writer2.IsOpen()) {
+    printf("File opened successfully\n");
+    writer2.Write("Content");
+} else {
+    printf("Failed to open file\n");
+}
+```
+
+## 相关文档
+
+- [FileWriter 总览](filewriter.md) - 返回类总览
+- [Open](Open.md) - 打开文件