refactor: improve test infrastructure and fix OpenGL GLAD initialization

- Rename D3D12Enum.h to D3D12Enums.h for naming consistency
- Fix OpenGL unit test GLAD initialization by using gladLoadGL()
  instead of gladLoadGLLoader(wglGetProcAddress) for fallback support
- Migrate remaining tests to use gtest_discover_tests for granular
  test discovery (math, core, containers, memory, threading, debug,
  components, scene, resources, input, opengl)
- Remove obsolete TEST_RESOURCES_DIR and copy_directory commands
  from OpenGL unit test CMakeLists (minimal/Res doesn't exist)
- Update TEST_SPEC.md with performance metrics and per-module
  build/test commands for faster development workflow
- Update CMake path references to use lowercase paths

docs/api/rhi/rhi.md

@@ -62,7 +62,7 @@ RHI 模块将上层渲染逻辑与底层图形 API 解耦，通过抽象接口
 
 | 类 | 文档 | 描述 |
 |----|------|------|
-| [RHIFence](rhi-fence/fence.md) | `RHIFence.h` | 同步栅栏，CPU/GPU 同步原语 |
+| [RHIFence](fence/fence.md) | `RHIFence.h` | 同步栅栏，CPU/GPU 同步原语 |
 | [RHIPipelineState](pipeline-state/pipeline-state.md) | `RHIPipelineState.h` | 管线状态对象，封装渲染管线配置 |
 | [RHISampler](sampler/sampler.md) | `RHISampler.h` | 纹理采样器，配置纹理过滤和寻址模式 |
 | [RHIPipelineLayout](pipeline-layout/pipeline-layout.md) | `RHIPipelineLayout.h` | 管线布局，定义着色器资源绑定布局 |