Below md a dashboard stacks to one column and dropped its rail. The rail is
now a horizontal row in the dashboard's own look, floated over the bottom
of the screen on /panel/{id} and above the dock in the app's view, with
44px items, sideways scrolling when it overflows, and padding so the last
tile clears it; a panel's read-only notice moves up out of its way. The
three looks share the geometry from ui/core.