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/workspace-patterns.tsx

@@ -17,7 +17,7 @@ export function WorkspaceHero({
   aside?: ReactNode;
 }) {
   return (
-    <AppCard level={3} layer="single">
+    <AppCard level={3}>
       <CardContent className="flex flex-col gap-4 p-6 lg:flex-row lg:items-end lg:justify-between lg:p-8">
         <div className="space-y-2">
           <p className="text-xs font-semibold uppercase tracking-[0.14em] text-muted-foreground">
@@ -40,7 +40,7 @@ export function WorkspaceSidebarPanel({
   children: ReactNode;
 }) {
   return (
-    <AppCard level={2} layer="single">
+    <AppCard level={2}>
       <CardHeader className="pb-4">
         <CardTitle className="text-base">{title}</CardTitle>
       </CardHeader>
@@ -100,7 +100,7 @@ export function WorkspaceLocaleCard({
   children: ReactNode;
 }) {
   return (
-    <AppCard level={2} layer="single">
+    <AppCard level={2}>
       <CardHeader className="pb-4">
         <CardTitle className="text-lg">{title}</CardTitle>
         <CardDescription>{hint}</CardDescription>