feat(services): update ServiceUnitCard with background color for FramePanel

- Added `bg-muted` class to FramePanel in ServiceUnitCard for improved visual consistency.
- Updated documentation to reflect the new background color setting for FramePanel, enhancing clarity on component usage.

apps/web/src/components/services/service-unit-card.tsx

@@ -49,6 +49,7 @@ import { cn } from '@cfdm/ui/lib/utils'
  * Preview: https://reui.io/preview/base/settings-8
  * Frame: https://reui.io/docs/components/base/frame
  * IconTile: https://reui.io/docs/components/base/icon-tile
+ * Header fill: FramePanel `bg-muted` (overrides `--frame-panel-bg`; see frame.tsx).
  */
 
 type LbMode = ServiceView['lb_mode']
@@ -124,7 +125,7 @@ export function ServiceUnitCard({
 
   return (
     <Frame stacked spacing="sm" className="h-full min-w-0">
-      <FramePanel fit>
+      <FramePanel fit className="bg-muted">
         <Item size="sm" className="w-full min-w-0 flex-nowrap border-0 p-0">
           <ItemMedia>
             <IconTile