feat: Add order auto-confirmation (best effort)

Added order confirmation after checkout completion.
Note: This requires MANAGE_ORDERS permission which currently
has the same bug as HANDLE_PAYMENTS. The try-catch ensures
checkout won't fail if confirmation fails. Orders will be
UNCONFIRMED until manually confirmed in dashboard.

src/lib/saleor/mutations/Checkout.ts

@@ -224,3 +224,19 @@ export const TRANSACTION_CREATE = gql`
     }
   }
 `;
+
+export const ORDER_CONFIRM = gql`
+  mutation OrderConfirm($orderId: ID!) {
+    orderConfirm(id: $orderId) {
+      order {
+        id
+        number
+        status
+      }
+      errors {
+        field
+        message
+      }
+    }
+  }
+`;