fix: 修复 D3D12SwapChain 重复创建 swapchain 问题

- 添加 Initialize(IDXGISwapChain*, width, height) 重载方法
- 接受已存在的 swapchain 而不是重复创建
- 测试通过，日志显示正常渲染

engine/include/XCEngine/RHI/D3D12/D3D12SwapChain.h

@@ -18,6 +18,7 @@ public:
     ~D3D12SwapChain();
 
     bool Initialize(IDXGIFactory4* factory, ID3D12CommandQueue* commandQueue, HWND windowHandle, uint32_t width, uint32_t height, uint32_t bufferCount = 2);
+    bool Initialize(IDXGISwapChain* swapChain, uint32_t width, uint32_t height);
     void Shutdown();
 
     uint32_t GetCurrentBackBufferIndex() const;

engine/src/RHI/D3D12SwapChain.cpp

@@ -47,6 +47,18 @@ bool D3D12SwapChain::Initialize(IDXGIFactory4* factory, ID3D12CommandQueue* comm
     return true;
 }
 
+bool D3D12SwapChain::Initialize(IDXGISwapChain* swapChain, uint32_t width, uint32_t height) {
+    HRESULT hResult = swapChain->QueryInterface(IID_PPV_ARGS(&m_swapChain));
+    if (FAILED(hResult)) {
+        return false;
+    }
+
+    m_width = width;
+    m_height = height;
+
+    return true;
+}
+
 void D3D12SwapChain::Shutdown() {
     m_swapChain.Reset();
 }