feat: render 2 rotating cubes side by side

- Push constant changed from float angle (4B) to mat4 model (64B)
- Two draw calls with different model matrices (x=-1.5 and x=+1.5)
- Both cubes rotate around Y axis at 0.2 rad/s
- 0 validation errors

src/Engine.Graphics.Vulkan/Shaders/triangle.vert

@@ -10,18 +10,11 @@ layout(row_major, set = 0, binding = 0) uniform CameraUBO {
     mat4 vp;
 };
 
-layout(push_constant) uniform PC {
-    float angle;
+layout(row_major, push_constant) uniform PC {
+    mat4 model;
 } pc;
 
 void main() {
-    float c = cos(pc.angle);
-    float s = sin(pc.angle);
-    vec3 rotated = vec3(
-        inPosition.x * c - inPosition.z * s,
-        inPosition.y,
-        inPosition.x * s + inPosition.z * c
-    );
-    gl_Position = vp * vec4(rotated, 1.0);
+    gl_Position = vp * pc.model * vec4(inPosition, 1.0);
     fragColor = inColor;
 }