Cell group radius token

Set the corner radius of containers that hold cells, such as the segmented Tabs track, with a new component token.

New features

• Added the cellGroup component radius token for containers that hold cells, such as the segmented Tabs track. It is exposed as --vortex-border-radius-cell-group and resolves to xs in Vortex, md in Awen and full in Sleek.
• Added --radius-cell-group to every theme's Tailwind file, which provides the rounded-cell-group utility.

Breaking changes

• Required the --vortex-border-radius-cell-group token in themes used with Vortex 0.18.0, where Tabs read it. Regenerate custom themes after upgrading.