Mobile auto-collapse target. Below 30rem of the stepper's own
container width, <cngx-stepper> falls back to one of the compact
variants instead of rendering the full strip. Set to 'off' to retain
the classic strip at every width.
The width itself is not configurable - it is a @container rule in
stepper-base.css, overridable in consumer CSS. This setting picks
what the strip collapses into, not where.