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/ui/app-card.tsx

@@ -87,10 +87,21 @@ export interface AppCardProps
     VariantProps<typeof appCardVariants>,
     VariantProps<typeof appCardInnerVariants> {
   layer?: "double" | "single";
+  /**
+   * Classes applied to the element that directly wraps `children` (the inner
+   * shell in `double` layer, the single shell in `single` layer). Use it for
+   * content utilities such as `space-y-*` / `grid` / `flex` so they keep
+   * working after switching a card to the layered (double) look, where
+   * `className` lands on the outer shell instead.
+   */
+  contentClassName?: string;
 }
 
 const AppCard = React.forwardRef<HTMLDivElement, AppCardProps>(
-  ({ className, level, padding, interactive, layer = "double", children, ...props }, ref) => {
+  (
+    { className, contentClassName, level, padding, interactive, layer = "double", children, ...props },
+    ref,
+  ) => {
     if (layer === "single") {
       return (
         <Card
@@ -102,6 +113,7 @@ const AppCard = React.forwardRef<HTMLDivElement, AppCardProps>(
               interactive,
             }),
             className,
+            contentClassName,
           )}
           {...props}
         >
@@ -129,6 +141,7 @@ const AppCard = React.forwardRef<HTMLDivElement, AppCardProps>(
               padding,
               interactive,
             }),
+            contentClassName,
           )}
         >
           {children}