feat: add Graphics module with D3D12 backend and documentation

Graphics Module:
- Add platform abstraction layer (GraphicsPlatformInterface)
- Add unified renderer entry point (Renderer)
- Add D3D12 backend implementation (D3D12Core, D3D12Interface)
- Add TestRenderer for multi-window rendering tests

Documentation:
- Add Graphics渲染架构分析.md
- Add D3D12学习Wiki.md
- Add changelogs directory with per-commit documentation
- Add 20260326-dx12-initial.md for initial framework
- Add 20260326-d3d12-foundation.md for Graphics module

Fixes:
- Resolve header include issues and type redefinition errors

EngineTest/TestRenderer.h

@@ -0,0 +1,15 @@
+/**
+ * @file TestRenderer.h
+ * @brief 渲染测试用例类声明。
+ */
+#pragma once
+#include "Test.h"
+
+
+class engine_test : public Test
+{
+public :
+	bool initialize() override;
+	void run() override;
+	bool shutdown() override;
+};