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-project-form.tsx

@@ -528,7 +528,7 @@ export function PortfolioProjectForm({
 
   if (!project && availableCategories.length === 0) {
     return (
-      <AppCard level={3} layer="single" padding="lg" className="rounded-surface">
+      <AppCard level={3} padding="lg" className="rounded-surface">
         <div className="space-y-4">
           <div className="space-y-2">
             <p className="text-xs uppercase tracking-[0.18em] text-muted-foreground">Portfolio Setup</p>
@@ -577,7 +577,7 @@ export function PortfolioProjectForm({
       <input ref={assetsInputRef} type="hidden" name="assets" value={assetsPayload} />
       <input ref={intentRef} type="hidden" name="intent" defaultValue="save" />
 
-      <AppCard level={3} layer="single" padding="lg" className="space-y-6">
+      <AppCard level={3} padding="lg" contentClassName="space-y-6">
         <div className="flex flex-col gap-6">
           <div className="flex flex-col gap-4 lg:flex-row lg:items-start lg:justify-between">
             <div className="space-y-3">
@@ -625,7 +625,7 @@ export function PortfolioProjectForm({
 
       <div className="space-y-6">
         <div>
-          <AppCard level={3} layer="single" padding="lg">
+          <AppCard level={3} padding="lg">
             <section className="space-y-6">
               <SectionHeader
                 title="Basic Information"
@@ -787,7 +787,7 @@ export function PortfolioProjectForm({
         </div>
 
         <div>
-          <AppCard level={3} layer="single" padding="lg">
+          <AppCard level={3} padding="lg">
             <section className="space-y-6">
               <SectionHeader
                 title="Localized Content"
@@ -838,7 +838,7 @@ export function PortfolioProjectForm({
         </div>
 
         <div>
-          <AppCard level={3} layer="single" padding="lg">
+          <AppCard level={3} padding="lg">
             <section className="space-y-6">
               <SectionHeader
                 title="Sections"
@@ -1028,7 +1028,7 @@ export function PortfolioProjectForm({
         </div>
 
         <div>
-          <AppCard level={3} layer="single" padding="lg">
+          <AppCard level={3} padding="lg">
             <div className="space-y-8">
               <div className="grid gap-4 lg:grid-cols-[minmax(0,1fr)_280px]">
                 <div className="space-y-6">
@@ -1203,7 +1203,7 @@ export function PortfolioProjectForm({
         </div>
       </div>
 
-      <AppCard level={3} layer="single" padding="lg">
+      <AppCard level={3} padding="lg">
         <div className="flex flex-col gap-4 md:flex-row md:items-center md:justify-end">
           <div className="flex flex-wrap items-center gap-3">
             {firstIncompleteStep ? (