Configure the mobile auto-collapse target for <cngx-stepper>. Below
30rem of the stepper's own container width, the classic strip swaps
to the chosen variant - 'text' (default) renders
<cngx-text-stepper>, 'dots' renders <cngx-dot-stepper>, 'off'
keeps the classic strip. The Material twin <cngx-mat-stepper> ignores
this setting.