fix: set language code before add to cart

Ensure language code is set in checkout store before creating checkout.
This ensures orders created from any page will have correct language.

- Add setLanguageCode to NewHero before addLine
- Add setLanguageCode to ProductDetail before addLine
- Uses current locale from useLocale or props

src/components/home/NewHero.tsx

@@ -15,9 +15,13 @@ interface NewHeroProps {
 
 export default function NewHero({ featuredProduct }: NewHeroProps) {
   const locale = useLocale();
-  const { addLine, openCart } = useSaleorCheckoutStore();
+  const { addLine, openCart, setLanguageCode } = useSaleorCheckoutStore();
 
   const handleAddToCart = async () => {
+    // Set language code before adding to cart
+    if (locale) {
+      setLanguageCode(locale);
+    }
     const variant = featuredProduct?.variants?.[0];
     if (variant?.id) {
       await addLine(variant.id, 1);