Badge's default look is a filled pill, right for status/picker chips
but wrong for an icon-only header button like the settings gear or
agent links trigger, which should read as chrome. Add variant='quiet'
(same naming/shape as Button's ButtonVariant) that drops the idle
background, keeping the existing hover/expanded feedback.
Apply it to the two icon-only Badge triggers: shared SettingsMenu
(used by both swarm-ui and the agent page) and the agent page's own
MetaNav links trigger. Add a components-page showcase sample so the
variant has a visible regression check going forward.