fix(ecommerce): deshabilitar compra y mostrar "Agotado" sin stock real

variant.available (calculado en lib/headless/providers/medusa.ts a
partir de manage_inventory/allow_backorder/inventory_quantity) ya
llegaba correcto hasta el componente, pero ningun boton de compra lo
usaba -- se podia seguir agregando al carrito un producto con stock 0.

Afecta product-purchase.tsx (pagina de producto), mobile-add-to-cart.tsx
(barra fija mobile) y product-card.tsx (tarjetas de catalogo): boton
deshabilitado + label "Agotado" en los tres, mas badge/overlay en la
tarjeta de catalogo.

workloads/ecommerce/components/product/product-card.tsx

@@ -24,7 +24,9 @@ export function ProductCard({ product, priority = false }: { product: Product; p
 
   const [selectedVariantId, setSelectedVariantId] = useState(product.variants[0]?.id);
   const selectedVariant = product.variants.find((variant) => variant.id === selectedVariantId) ?? product.variants[0];
+  const outOfStock = selectedVariant?.available === false;
   const lowStock =
+    !outOfStock &&
     selectedVariant?.inventoryQuantity !== null &&
     selectedVariant?.inventoryQuantity !== undefined &&
     selectedVariant.inventoryQuantity > 0 &&
@@ -36,7 +38,8 @@ export function ProductCard({ product, priority = false }: { product: Product; p
     <article className="group flex h-full flex-col overflow-hidden rounded-lg border border-slate-100 bg-white shadow-lg shadow-ari-marino/5 transition duration-300 hover:-translate-y-1.5 hover:shadow-2xl hover:shadow-ari-coral/10">
       <div className="relative aspect-square overflow-hidden bg-white">
         <Link href={`/product/${product.slug}`} prefetch={false}><Image src={product.thumbnail} alt={product.name} fill priority={priority} sizes="(max-width: 640px) 82vw, (max-width: 1024px) 44vw, 280px" className="object-cover transition duration-500 group-hover:scale-[1.035]" /></Link>
-        <div className="absolute left-3 top-3 flex gap-2">{discountPercent && discountPercent > 0 && <Badge className="bg-ari-coral-claro text-ari-marino">-{discountPercent}%</Badge>}{product.isNew && <Badge className="bg-ari-marino text-white">Nuevo</Badge>}{product.featured && <Badge className="bg-ari-coral-claro text-ari-marino"><Sparkles className="mr-1 size-3" />Top</Badge>}</div>
+        <div className="absolute left-3 top-3 flex gap-2">{outOfStock && <Badge className="bg-rose-600 text-white">Agotado</Badge>}{discountPercent && discountPercent > 0 && <Badge className="bg-ari-coral-claro text-ari-marino">-{discountPercent}%</Badge>}{product.isNew && <Badge className="bg-ari-marino text-white">Nuevo</Badge>}{product.featured && <Badge className="bg-ari-coral-claro text-ari-marino"><Sparkles className="mr-1 size-3" />Top</Badge>}</div>
+        {outOfStock && <div className="pointer-events-none absolute inset-0 bg-white/40" />}
         <button type="button" aria-label={isFavorite ? "Quitar de favoritos" : "Agregar a favoritos"} aria-pressed={isFavorite} className={`absolute right-3 top-3 rounded-full p-2.5 shadow-lg backdrop-blur transition ${isFavorite ? "bg-ari-coral text-white" : "bg-white/95 text-slate-900 hover:text-ari-coral"}`} onClick={() => toggleProduct(product)}><Heart className={`size-4 ${isFavorite ? "fill-current" : ""}`} /></button>
       </div>
       <div className="flex flex-1 flex-col space-y-3 p-5">
@@ -67,12 +70,15 @@ export function ProductCard({ product, priority = false }: { product: Product; p
         {lowStock !== null && (
           <span className="flex items-center gap-1.5 text-xs font-bold text-amber-600"><TriangleAlert className="size-3.5" />Quedan {lowStock}</span>
         )}
+        {outOfStock && (
+          <span className="flex items-center gap-1.5 text-xs font-bold text-rose-600"><TriangleAlert className="size-3.5" />Sin stock</span>
+        )}
         <div className="mt-auto flex items-center justify-between gap-3 pt-1">
           <div className="flex flex-col">
             {product.compareAtPrice && <span className="text-xs font-bold text-slate-400 line-through">{formatMoney(product.compareAtPrice, product.currency)}</span>}
             <strong className="font-display text-base font-bold text-ari-marino">{formatMoney(product.price, product.currency)}</strong>
           </div>
-          <Button variant="primary" size="sm" onClick={() => addItem(product, selectedVariantId)}><ShoppingBag className="size-4" />Agregar</Button>
+          <Button variant="primary" size="sm" disabled={outOfStock} onClick={() => addItem(product, selectedVariantId)}><ShoppingBag className="size-4" />{outOfStock ? "Agotado" : "Agregar"}</Button>
         </div>
       </div>
     </article>