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/public/mock/product-12.svg

@@ -0,0 +1,7 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="400" height="400" viewBox="0 0 400 400">
+  <defs><linearGradient id="g" x1="0" y1="0" x2="1" y2="1">
+    <stop offset="0" stop-color="#6a1b9a"/><stop offset="1" stop-color="#ab47bc"/>
+  </linearGradient></defs>
+  <rect width="400" height="400" fill="url(#g)"/>
+  <text x="200" y="200" font-family="system-ui,sans-serif" font-size="50" fill="rgba(255,255,255,.9)" text-anchor="middle" dominant-baseline="middle">P12</text>
+</svg>