OpenGL: Add minimal integration test and enable integration test framework

- Add OpenGL_Minimal integration test using Win32 native API + glad
- Copy run_integration_test.py and compare_ppm.py from D3D12
- Create minimal/main.cpp with red clear color (matching D3D12)
- Generate GT.ppm golden template for 1280x720 red window
- Add VertexArray_Bind_MultipleAttributes unit test
- Update integration/CMakeLists.txt to build OpenGL_Minimal target

tests/RHI/OpenGL/unit/test_vertex_array.cpp

@@ -68,3 +68,48 @@ TEST_F(OpenGLTestFixture, VertexArray_Bind_Unbind) {
     
     vao.Shutdown();
 }
+
+TEST_F(OpenGLTestFixture, VertexArray_Bind_MultipleAttributes) {
+    OpenGLVertexArray vao;
+    vao.Initialize();
+    
+    OpenGLBuffer buffer1;
+    float positions[] = { 0.0f, 0.0f, 0.5f, 0.5f };
+    buffer1.InitializeVertexBuffer(positions, sizeof(positions));
+    
+    OpenGLBuffer buffer2;
+    float colors[] = { 1.0f, 0.0f, 0.0f, 1.0f };
+    buffer2.InitializeVertexBuffer(colors, sizeof(colors));
+    
+    VertexAttribute attrPos;
+    attrPos.index = 0;
+    attrPos.count = 2;
+    attrPos.type = GL_FLOAT;
+    attrPos.normalized = false;
+    attrPos.stride = sizeof(float) * 2;
+    attrPos.offset = 0;
+    
+    VertexAttribute attrColor;
+    attrColor.index = 1;
+    attrColor.count = 4;
+    attrColor.type = GL_FLOAT;
+    attrColor.normalized = false;
+    attrColor.stride = sizeof(float) * 4;
+    attrColor.offset = 0;
+    
+    vao.AddVertexBuffer(buffer1.GetID(), attrPos);
+    vao.AddVertexBuffer(buffer2.GetID(), attrColor);
+    
+    vao.Bind();
+    GLint boundVAO = 0;
+    glGetIntegerv(GL_VERTEX_ARRAY_BINDING, &boundVAO);
+    EXPECT_EQ(boundVAO, static_cast<GLint>(vao.GetID()));
+    
+    vao.Unbind();
+    glGetIntegerv(GL_VERTEX_ARRAY_BINDING, &boundVAO);
+    EXPECT_EQ(boundVAO, 0);
+    
+    buffer1.Shutdown();
+    buffer2.Shutdown();
+    vao.Shutdown();
+}