fix: encapsulate OpenGL types in VertexAttribute to eliminate raw GL API usage in tests

- Add VertexAttributeType and VertexAttributeNormalized enums in OpenGLVertexArray.h
- Add ToGLAttributeType() converter in OpenGLVertexArray.cpp
- Remove glActiveTexture() call from quad test (already handled by texture.Bind())
- Remove #include <glad/glad.h> from triangle test
- Update unit tests to use encapsulated enums

All three OpenGL integration tests (minimal, triangle, quad) pass with 0% pixel difference.

tests/RHI/OpenGL/unit/test_command_list.cpp

@@ -54,8 +54,8 @@ TEST_F(OpenGLTestFixture, CommandList_Draw_VAO) {
     VertexAttribute attr;
     attr.index = 0;
     attr.count = 3;
-    attr.type = GL_FLOAT;
-    attr.normalized = false;
+    attr.type = VertexAttributeType::Float;
+    attr.normalized = VertexAttributeNormalized::False;
     attr.stride = sizeof(float) * 3;
     attr.offset = 0;
     vao.AddVertexBuffer(vbo.GetID(), attr);