feat: 实现D3D12 RHI抽象层，修复PSO创建问题

- 添加RHI接口定义(IRHIDevice, ICommandList, IResource等)
- 实现D3D12Device, D3D12CommandList, D3D12PipelineState等
- 修复RootSignature参数数量(3->4)与HelloEarth一致
- 修复DSV格式设置(Unknown->D24_UNorm_S8_UInt)
- 添加Geometry Shader编译
- 创建XCEngineDemo项目验证RHI功能

engine/CMakeLists.txt

@@ -80,8 +80,25 @@ add_library(XCEngine STATIC
     src/Debug/FileLogSink.cpp
     src/Debug/Logger.cpp
     src/Debug/Profiler.cpp
+
+    # RHI
+    include/XCEngine/RHI/RHIDefines.h
+    include/XCEngine/RHI/IRHIResources.h
+    include/XCEngine/RHI/ICommandList.h
+    include/XCEngine/RHI/IRHIDevice.h
+    include/XCEngine/RHI/IResourceViews.h
+    include/XCEngine/RHI/RHISystem.h
+
+    # Rendering
+    include/XCEngine/Rendering/Resources.h
+    include/XCEngine/Rendering/RenderTarget.h
+    include/XCEngine/Rendering/Shader.h
+    include/XCEngine/Rendering/RenderContext.h
+    include/XCEngine/Rendering/StaticMeshComponent.h
 )
 
+add_subdirectory(src/RHI/D3D12)
+
 target_include_directories(XCEngine PUBLIC
     ${CMAKE_CURRENT_SOURCE_DIR}/include
     ${CMAKE_CURRENT_SOURCE_DIR}/include/XCEngine