feat(ui): spring the active pill in tab strips

Give the active-pill tab strips the lifted, physical feel of a spring
capsule: the pill now travels with a slight overshoot instead of jumping,
leans toward a neighbouring tab on press, and sits on a raised surface with
a soft ambient shadow rather than a hard border.

Transitions are opt-in per switch so first measurement and container
resizes still snap into place, and reduced-motion disables them.

Also drop the icons from the git commit/update/pr switcher, along with the
now-unused iconOnlyActiveTab prop.

packages/ui/src/components/views/git/GitHeader.tsx

@@ -374,7 +374,6 @@ export const GitHeader: React.FC<GitHeaderProps> = ({
               onSelect={onSelectActionTab}
               layoutMode="fit"
               variant="active-pill"
-              iconOnlyActiveTab={true}
               activePillButtonClassName="h-7"
               className="h-full"
             />