Step — Indicator

Everything the indicator prop accepts: the auto default, an always-number badge, a custom ReactNode, and none, each on its own completed Step so the prop is the only difference between them. Every variant occupies the same 16px box, so a step swapping its number for a check as it completes never shifts the label beside it. The last cell shows that a custom node can be live rather than static: a Spinner on a step that is in progress, shaded `inherit` so it picks up the step's own tint like any other glyph.