STYLED - Roll out the layered card system to the admin workspace

The double-layer AppCard look showcased in the UI Kit was only applied on
the public frontend; every admin surface was pinned to layer=single and
stayed flat. Convert the admin section/container cards to the default
layered look, keeping compact metric tiles, toolbars, image tiles and
nested leaf cards single.

Add AppCard contentClassName so content utilities (space-y-*, grid, flex)
keep applying to the inner shell after the switch to double layer.

components/admin/marquee-settings-form.tsx

@@ -29,7 +29,7 @@ export function MarqueeSettingsForm({
 
       <div className="grid gap-4 xl:grid-cols-4">
         {rowMeta.map((row) => (
-          <AppCard key={`de-${row.key}`} level={2} layer="single" padding="sm" className="space-y-2">
+          <AppCard key={`de-${row.key}`} level={2} padding="sm" contentClassName="space-y-2">
             <Label htmlFor={`${row.key}-de`} className="text-sm font-semibold text-foreground">{row.label}</Label>
             <Textarea
               id={`${row.key}-de`}