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/unit/test_device.cpp

@@ -1,4 +1,5 @@
 #include "fixtures/RHITestFixture.h"
+#include "XCEngine/RHI/OpenGL/OpenGLDevice.h"
 
 using namespace XCEngine::RHI;
 
@@ -10,9 +11,15 @@ TEST_P(RHITestFixture, Device_Initialize_Shutdown) {
     RHIDevice* device = RHIFactory::CreateRHIDevice(GetBackendType());
     ASSERT_NE(device, nullptr);
 
-    RHIDeviceDesc desc = {};
-    desc.enableDebugLayer = true;
-    bool initResult = device->Initialize(desc);
+    bool initResult = false;
+    if (GetBackendType() == RHIType::D3D12) {
+        RHIDeviceDesc desc = {};
+        desc.enableDebugLayer = true;
+        initResult = device->Initialize(desc);
+    } else if (GetBackendType() == RHIType::OpenGL) {
+        auto* oglDevice = static_cast<OpenGLDevice*>(device);
+        initResult = oglDevice->InitializeWithExistingWindow(GetWindowHandle());
+    }
     ASSERT_TRUE(initResult);
 
     device->Shutdown();