cornerZone property
Continuous-corner zone, as a multiple of the corner radius.
Above 1 a rectangle's corner curve starts cornerZone × radius from
the corner (capped at half the shorter side) and is a superellipse
whose exponent is derived so it passes through the circular arc's 45°
point, like Apple's continuous corners; it becomes a circular arc when
the zone clamps to the radius (pills). 1 keeps cornerExponent with
the curve starting at the radius. Applies to the outline only; capsules
and circles stay exact circles. Fitted, not measured: see
docs/superpowers/notes/fidelity-status.md (Task A1).
Implementation
final double cornerZone;