D3D12: Add Quad integration test with texture sampling

- Add quad test that renders a textured quad with earth texture
- Add quad.hlsl shader with texture sampling (Texture2D + SamplerState)
- Add SRV descriptor heap and root signature with SRV table
- Fix MessageBox errors -> Log() console output
- Fix shader float2->float4 type mismatch
- Fix texture initialization to use proper command list handling
- Add shader error output to stderr in D3D12Shader
- Add Map error logging in D3D12Screenshot

engine/src/RHI/D3D12/D3D12Screenshot.cpp

@@ -159,6 +159,7 @@ bool D3D12Screenshot::CopyToReadbackAndSave(ID3D12Device* device,
     unsigned char* mappedData = nullptr;
     hr = readbackBuffer->Map(0, &readRange, (void**)&mappedData);
     if (FAILED(hr)) {
+        XCEngine::Debug::Logger::Get().Error(XCEngine::Debug::LogCategory::Rendering, "Screenshot: Map failed");
         cmdList->Release();
         cmdAlloc->Release();
         readbackBuffer->Release();

engine/src/RHI/D3D12/D3D12Shader.cpp

@@ -20,6 +20,7 @@ bool D3D12Shader::CompileFromFile(const wchar_t* filePath, const char* entryPoin
         if (m_error) {
             const char* errorMsg = static_cast<const char*>(m_error->GetBufferPointer());
             OutputDebugStringA(errorMsg);
+            fprintf(stderr, "[SHADER ERROR] %s\n", errorMsg);
         }
         return false;
     }