badge: add a quiet variant for icon-only header triggers

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.

frontend/packages/agent/src/components/MetaNav.tsx

@@ -14,6 +14,11 @@
 // link and rebuild; rebuild's gone outright, the dashboard's own
 // R3BU1LD button already covers it, dashboard-link moves here, so
 // `OverflowMenu` had nothing left to justify existing and is deleted).
+//
+// `variant="quiet"` — mara: "link and settings button should not have
+// the badge bg". `Badge`'s default filled-pill look is right for a
+// status/picker chip, wrong for this icon-only trigger, which should
+// read as header chrome. See `@hive/shared/badge.js`'s `BadgeVariant`.
 
 // v1 of this rendered every link inline in the header's title row —
 // mara, live: "the login card looks like it is behind the header"
@@ -73,7 +78,13 @@ export function MetaNav({ links, forgePublicUrl, dashboardBase }: MetaNavProps)
 
   return (
     <div class="meta-nav-anchor" ref={rootRef}>
-      <Badge value={<LinkIcon />} title="agent links" onClick={() => setOpen((o) => !o)} expanded={open} />
+      <Badge
+        value={<LinkIcon />}
+        title="agent links"
+        variant="quiet"
+        onClick={() => setOpen((o) => !o)}
+        expanded={open}
+      />
       {open ? (
         <div class="meta-nav-popover" role="menu" aria-label="agent links">
           <a