Check stock for Shop's add to cart button

src/components/layouts/PosterLayout.svelte

@@ -10,6 +10,8 @@
     export let product: any
     export let shopProduct: any
 
+    $: hasStock = shopProduct.stock_level > 0
+
 
     /**
      * Preview photos specs
@@ -69,8 +71,10 @@
                 <dd>{shopProduct.name} – {shopProduct.price}€</dd>
             </dl>
             <Button
-                text="Add to cart"
+                tag="button"
+                text={hasStock ? 'Add to cart' : 'Sold out'}
                 color="pinklight"
+                disabled={!hasStock}
                 on:click={() => addToCart($cartId, shopProduct)}
             />
         </div>