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/nuxt.config.ts

@@ -1,11 +1,12 @@
 export default defineNuxtConfig({
   modules: ["@pinia/nuxt", "@nuxtjs/i18n"],
-  css: ["@vmall/shared/ui.css"],
+  css: ["@vmall/shared/ui.css", "~/assets/mall.css"],
   devtools: { enabled: false },
   devServer: { port: 3000 },
   runtimeConfig: {
     public: {
       apiBase: "http://localhost:8080/api",
+      mockApi: true,
       appName: "mall",
     },
   },