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/components/ui/Breadcrumb.vue

@@ -0,0 +1,35 @@
+<script setup lang="ts">
+defineProps<{ items: { label: string; to?: string }[] }>();
+</script>
+
+<template>
+  <nav class="crumbs w1200" aria-label="breadcrumb">
+    <template v-for="(item, i) in items" :key="i">
+      <NuxtLink v-if="item.to" :to="item.to">{{ item.label }}</NuxtLink>
+      <span v-else class="here">{{ item.label }}</span>
+      <span v-if="i < items.length - 1" class="sep">/</span>
+    </template>
+  </nav>
+</template>
+
+<style scoped>
+.crumbs {
+  margin: 20px auto;
+  font-size: 13px;
+  color: var(--mall-muted);
+}
+a {
+  color: var(--mall-muted);
+  text-decoration: none;
+}
+a:hover {
+  color: var(--mall-red);
+}
+.sep {
+  margin: 0 8px;
+  color: var(--mall-faint);
+}
+.here {
+  color: var(--mall-ink);
+}
+</style>