Function move_node 

pub fn move_node(
    root: &mut LayoutNode,
    node_id: &str,
    new_parent_id: &str,
    index: usize,
) -> Result<(), LayoutError>

Move the node identified by node_id to be the child at index under the node identified by new_parent_id. Resets the moved node’s size to DEFAULT_NODE_SIZE unless it stays under the same parent.