Hide the free-shipping progress banner when the cart has no shippable items

Reuses FreeShippingBanner's existing threshold===null early return —
a "€X bis kostenlosem Versand" nudge makes no sense for a cart that was
never going to be charged shipping.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/cart/components/CartContent.tsx

@@ -170,7 +170,12 @@ export function CartContent({
       ) : (
         <>
         <div className="pt-2 px-[var(--layout-padding-x)] w-full">
-          <FreeShippingBanner subtotal={subtotal} threshold={freeShippingThreshold} />
+          {/* threshold forced to null (banner just doesn't render, see its
+              own early return) whenever nothing in the cart actually
+              triggers shipping — a "€X bis kostenlosem Versand" nudge
+              makes no sense for a cart that was never going to be charged
+              shipping in the first place. */}
+          <FreeShippingBanner subtotal={subtotal} threshold={cartHasShippableItem(items) ? freeShippingThreshold : null} />
         </div>
         <div className="flex flex-col lg:flex-row gap-8 lg:gap-10 items-start pb-10 pt-4 px-[var(--layout-padding-x)] w-full">
           {/* Cart card — lg:-only split from the sidebar (same "wide content