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/debug/filelogsink/flush.md

@@ -0,0 +1,24 @@
+# FileLogSink::Flush
+
+```cpp
+void Flush() override
+```
+
+刷新文件缓冲区，调用底层 `FileWriter` 的 flush 方法确保所有待写入的日志数据已实际写入磁盘。
+
+**复杂度：** O(1)
+
+**示例：**
+
+```cpp
+auto fileSink = std::make_unique<XCEngine::Debug::FileLogSink>("logs/app.log");
+XCEngine::Debug::Logger::Get().AddSink(std::move(fileSink));
+// 关键操作后立即刷新
+XCEngine::Debug::Logger::Get().Info(XCEngine::Debug::LogCategory::General, "Checkpoint saved");
+// 确保写入磁盘
+XCEngine::Debug::Logger::Get().Flush();
+```
+
+## 相关文档
+
+- [FileLogSink 总览](filelogsink.md) - 返回类总览