Center & Span the red rectangle to be a banner

Figured out how to place nodes in the grid. This will eventually become
the banner that says what the machine does.

src/widgets.rs

@@ -11,7 +11,11 @@ pub fn spawn_cutter_machine_ui(mut commands: Commands) {
     machine_ui_base(),
     children![
       (
-        Node::default(), // TODO: A real node with stuff in it (buttons, maybe?)
+        // TODO: A real node with stuff in it (buttons, maybe?)
+        Node {
+          grid_column: GridPlacement::start_span(2, 3),
+          ..default()
+        },
         BackgroundColor(RED.into()),
         Pickable::default()
       ),