Function spawn_plane 

pub fn spawn_plane<'a>(
    world: &'a mut GameWorld,
    size: f32,
    y: f32,
) -> Vessel<'a>

Creates a Vessel with a plane mesh at the origin.

Attaches an authored MeshRef::Procedural; the asset resolver rebuilds the plane geometry and mints the runtime HandleComponent<Mesh> before the GPU mesh projection runs.