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/OpenGL/integration/triangle/main.cpp

@@ -86,13 +86,7 @@ int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine
     RenderDocCapture::Get().SetCaptureFilePath(".\\triangle_frame30");
 
     OpenGLDevice device;
-    RHIDeviceDesc desc = {};
-    desc.windowHandle = hwnd;
-    desc.width = gWidth;
-    desc.height = gHeight;
-    desc.appName = L"OpenGL_Triangle_Test";
-    desc.enableDebugLayer = true;
-    if (!device.Initialize(desc)) {
+    if (!device.InitializeWithExistingWindow(hwnd)) {
         Log("[ERROR] Failed to initialize OpenGL device");
         return -1;
     }