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/threading/mutex/unlock-const.md

@@ -0,0 +1,34 @@
+# Mutex::unlock
+
+```cpp
+void unlock() const;
+```
+
+释放互斥锁（const 版本），允许其他等待中的线程获取该锁。
+
+**参数：** 无
+
+**返回：** 无
+
+**线程安全：** ✅
+
+**复杂度：** O(1)
+
+**示例：**
+
+```cpp
+#include "XCEngine/Threading/Mutex.h"
+
+XCEngine::XCEngine::Threading::Mutex mtx;
+std::vector<int> data;
+
+void SafePush(int value) {
+    mtx.lock();
+    data.push_back(value);
+    mtx.unlock();
+}
+```
+
+## 相关文档
+
+- [Mutex 总览](mutex.md) - 返回类总览