feat(emails): implement transactional email system with Resend

- Add Resend email integration with @react-email/render
- Create email templates: OrderConfirmation, OrderShipped, OrderCancelled, OrderPaid
- Implement webhook handler for ORDER_CREATED and other events
- Add multi-language support for customer emails
- Admin emails in English with order details
- Update checkout page with auto-scroll on order completion
- Configure DASHBOARD_URL environment variable

src/lib/saleor/mutations/Checkout.ts

@@ -152,3 +152,24 @@ export const CHECKOUT_EMAIL_UPDATE = gql`
   }
   ${CHECKOUT_FRAGMENT}
 `;
+
+export const CHECKOUT_METADATA_UPDATE = gql`
+  mutation CheckoutMetadataUpdate($checkoutId: ID!, $metadata: [MetadataInput!]!) {
+    updateMetadata(id: $checkoutId, input: $metadata) {
+      item {
+        ... on Checkout {
+          id
+          metadata {
+            key
+            value
+          }
+        }
+      }
+      errors {
+        field
+        message
+        code
+      }
+    }
+  }
+`;