Add gift card payment method display in order transactions

Add GiftCardPaymentMethod component to display Saleor gift card
payment details (icon + masked code) in order transaction cards.
Update GraphQL fragment to fetch SaleorGiftcardPaymentMethodDetails
with code field. Add Storybook story for the new payment method.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: lkostrowski

schema-main.graphql

@@ -642,6 +642,11 @@ export const transactionItemFragment = gql`
     lastDigits
   }
 
+  fragment SaleorGiftcardPaymentMethodDetails on SaleorGiftcardPaymentMethodDetails {
+    name
+    code
+  }
+
   fragment TransactionItem on TransactionItem {
     ...TransactionBaseItem
     pspReference
@@ -666,6 +671,9 @@ export const transactionItemFragment = gql`
       ... on OtherPaymentMethodDetails {
         ...OtherPaymentMethodDetails
       }
+      ... on SaleorGiftcardPaymentMethodDetails {
+        ...SaleorGiftcardPaymentMethodDetails
+      }
     }
     events {
       ...TransactionEvent