fix: improve doc link navigation and tree display

- Fix link resolution with proper relative/absolute path handling
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docs/api/rhi/d3d12/descriptor-heap/get-gpu-descriptor-handle-for-heap-start.md

@@ -0,0 +1,15 @@
+# D3D12DescriptorHeap::GetGPUDescriptorHandleForHeapStart
+
+```cpp
+D3D12_GPU_DESCRIPTOR_HANDLE GetGPUDescriptorHandleForHeapStart() const;
+```
+
+获取堆起始处的 GPU 描述符句柄。
+
+**返回：** GPU 描述符句柄
+
+**复杂度：** O(1)
+
+## 相关文档
+
+- [D3D12DescriptorHeap 总览](descriptor-heap.md) - 返回类总览