refactor: Migrate ViewCube to shader-based rendering

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

src/shaders/texture.vert

@@ -0,0 +1,15 @@
+#version 330 core
+
+layout (location = 0) in vec3 aPos;
+layout (location = 1) in vec2 aTexCoord;
+
+out vec2 TexCoord;
+
+uniform mat4 modelViewMatrix;
+uniform mat4 projectionMatrix;
+
+void main()
+{
+    gl_Position = projectionMatrix * modelViewMatrix * vec4(aPos, 1.0);
+    TexCoord = aTexCoord;
+}