refactor: Migrate ViewportWidget to shader-based OpenGL rendering (FFP disabled)

Co-authored-by: aider (gemini/gemini-2.5-pro) <aider@aider.chat>

src/shaders/shaders.qrc

@@ -0,0 +1,6 @@
+<RCC>
+    <qresource prefix="/shaders">
+        <file>simple.vert</file>
+        <file>simple.frag</file>
+    </qresource>
+</RCC>

src/shaders/simple.frag

@@ -0,0 +1,10 @@
+#version 330 core
+
+out vec4 FragColor;
+
+uniform vec4 objectColor;
+
+void main()
+{
+    FragColor = objectColor;
+}

src/shaders/simple.vert

@@ -0,0 +1,11 @@
+#version 330 core
+
+layout (location = 0) in vec3 aPos;
+
+uniform mat4 modelViewMatrix;
+uniform mat4 projectionMatrix;
+
+void main()
+{
+    gl_Position = projectionMatrix * modelViewMatrix * vec4(aPos, 1.0);
+}