axis: state-dependent radius (press morph)

[mehdibha]

What

Radius that responds to interaction state — Material 3's press morph (a pressed control's corners tighten/relax with an animation) is the canonical example.

Why

Needed for a high-fidelity Material-style preset; part of the "recreate almost any design system" bar.

Notes

• Deferred from the radius-ladder work (PRs feat(www): resolve styles.css surface vars on publish #573–feat(www): derive radius ladder from a base length token #575). No shadcn style does this; zero parity pressure — purely for preset fidelity.
• Mechanics sketch: a data-pressed radius var swap + transition-[border-radius] on control roles (proposal: radius role layer (control/item/surface/panel) + pill #579); must respect prefers-reduced-motion.
• Blocked on nothing, but sensibly sequenced after proposal: radius role layer (control/item/surface/panel) + pill #579 so it targets roles, not components.