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

tests/RHI/D3D12/integration/triangle/main.cpp

@@ -84,9 +84,6 @@ LRESULT CALLBACK WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam) {
 
 bool InitD3D12() {
     RHIDeviceDesc deviceDesc;
-    deviceDesc.windowHandle = gHWND;
-    deviceDesc.width = gWidth;
-    deviceDesc.height = gHeight;
     deviceDesc.adapterIndex = 0;
     deviceDesc.enableDebugLayer = false;
     deviceDesc.enableGPUValidation = false;