feat: persist customer product and shop favorites through the live API

Replace mall fixture favorites with customer-scoped endpoints, and send signed-out shoppers back to the page they left after sign-in.

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/mall/pages/integral.vue

@@ -11,6 +11,7 @@ import { ApiError, t as pick } from "@vmall/shared";
 const { locale, t } = useI18n();
 const { $api } = useNuxtApp();
 const session = useSessionStore();
+const signInThenReturn = useSignInRedirect();
 const stats = ref<AccountSummary | null>(null);
 const products = ref<IntegralProduct[]>([]);
 const redemptions = ref<IntegralOrder[]>([]);
@@ -85,7 +86,7 @@ function addressForRedemption(): Address | null {
 
 async function redeem(product: IntegralProduct): Promise<void> {
   if (!session.isLoggedIn) {
-    await navigateTo("/login");
+    await signInThenReturn();
     return;
   }
   const address = addressForRedemption();