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/portfolio-categories-manager.tsx

@@ -110,7 +110,7 @@ function CategoryLocaleFields({
           const descriptionKey = `description${locale.key}` as const;
 
           return (
-            <AppCard key={`${idPrefix}-${locale.key}`} level={2} layer="single" padding="sm" className="space-y-4 rounded-nested">
+            <AppCard key={`${idPrefix}-${locale.key}`} level={2} padding="sm" className="rounded-nested" contentClassName="space-y-4">
               <p className="text-sm font-medium text-foreground">{locale.label}</p>
 
               <div className="space-y-2">
@@ -168,7 +168,7 @@ function CategoryStatusFields({
       </div>
 
       <div className="grid gap-4 lg:grid-cols-[minmax(0,1fr)_220px]">
-        <AppCard level={2} layer="single" padding="sm" className="rounded-nested">
+        <AppCard level={2} padding="sm" className="rounded-nested">
           <div className="flex items-start gap-3">
             {isActive ? (
               <ShieldCheck className="mt-0.5 h-4 w-4 text-status-success" />
@@ -395,7 +395,7 @@ export function PortfolioCategoriesManager({
               <DialogDescription>{copy.modalDescription}</DialogDescription>
             </DialogHeader>
 
-            <AppCard level={2} layer="single" padding="sm" className="rounded-nested">
+            <AppCard level={2} padding="sm" className="rounded-nested">
               <div className="grid gap-3 sm:grid-cols-3">
                 <div className="space-y-1">
                   <p className="text-sm font-medium text-foreground">1. Basics</p>
@@ -426,7 +426,7 @@ export function PortfolioCategoriesManager({
         </Dialog>
       </div>
 
-      <AppCard level={3} layer="single">
+      <AppCard level={3}>
         <CardContent className="space-y-4 p-6">
           <div className="flex items-center gap-3">
             <Layers3 className="h-5 w-5 text-brand-primary" />