refactor(RHI): 将窗口职责从RHI移到Platform层

- RHIDeviceDesc 删除 windowHandle/width/height/appName
- SwapChainDesc 添加 windowHandle 字段
- RHISwapChain 删除 PollEvents/ShouldClose/SetFullscreen 等窗口相关接口
- OpenGLDevice 删除 CreateRenderWindow，改用 InitializeWithExistingWindow
- 更新所有集成测试使用新API
- 273个单元测试 + 8个集成测试全部通过

engine/src/RHI/D3D12/D3D12Device.cpp

@@ -335,7 +335,7 @@ RHIFence* D3D12Device::CreateFence(const FenceDesc& desc) {
 
 RHISwapChain* D3D12Device::CreateSwapChain(const SwapChainDesc& desc) {
     auto* swapChain = new D3D12SwapChain();
-    HWND hwnd = static_cast<HWND>(m_deviceDesc.windowHandle);
+    HWND hwnd = static_cast<HWND>(desc.windowHandle);
     if (swapChain->Initialize(m_factory.Get(), m_commandQueue.Get(), hwnd,
                               desc.width, desc.height, desc.bufferCount)) {
         return swapChain;