Function constrain_auto_grid_track_items 

pub fn constrain_auto_grid_track_items(node: &mut LayoutNode) -> bool

Bug fix: grid-template-columns, width

During the intrinsic grid pass ui_layout measures block flex containers with their containing width. In a template such as 1fr auto 1fr, that makes the auto track take the entire grid and leaves both fraction tracks at zero. The first layout still records the flex contents’ actual extent in children_box, so use that intrinsic width and let a second layout resolve the tracks correctly.