feat(mall): classic B2B2C PC storefront with fixed mock API layer

- Mock adapter implementing @vmall/shared ApiClient (localStorage-persisted
  cart/orders/invoices), runtime switch via mockApi flag (default on)
- Fixed bilingual mock catalog: 3-level categories, 24 products w/ SKUs,
  stores, brands, banners, floors, seckill/collective/integral, comments,
  coupons, addresses, seeded orders/shipments/invoices
- B2B2C mall shell: top bar, logo/search/cart header, dark nav + category
  mega-menu, value-prop footer, back-to-top; 1200px grid, #ca151e theme
- UI primitives replacing element-plus: carousel, pagination, breadcrumb,
  qty stepper, rating stars, modal, tabs, step bar, product card
- Pages: home floors, search (filters/sort/paging), goods detail (SKU
  picker, store rail, review tabs), cart -> checkout -> pay -> success,
  auth pages, user center (dashboard/orders/addresses/favorites/coupons/
  invoices), stores, seckill, collective, integral
- i18n split into per-domain locale modules (en+zh)
- OpenSpec change mall-pc-storefront-replica archived; all specs green

apps/mall/plugins/api.ts

@@ -1,10 +1,16 @@
 import { createApi } from "@vmall/shared";
+import { createMockApi } from "~/mock/api";
 
 export default defineNuxtPlugin(() => {
   const config = useRuntimeConfig();
-  const api = createApi({
-    baseUrl: config.public.apiBase as string,
-    getToken: () => (import.meta.client ? localStorage.getItem("vmall.token") : null),
-  });
+  // Mock-first MVP: default to the fixed-data adapter; set NUXT_PUBLIC_MOCK_API=false
+  // (or runtimeConfig.public.mockApi) to talk to the live backend again.
+  const useMock = (config.public.mockApi as boolean | undefined) !== false;
+  const api = useMock
+    ? createMockApi()
+    : createApi({
+        baseUrl: config.public.apiBase as string,
+        getToken: () => (import.meta.client ? localStorage.getItem("vmall.token") : null),
+      });
   return { provide: { api } };
 });