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/EmptyState.vue

@@ -0,0 +1,22 @@
+<script setup lang="ts">
+withDefaults(defineProps<{ text?: string }>(), { text: "" });
+</script>
+
+<template>
+  <div class="empty">
+    <div class="icon">∅</div>
+    <p>{{ text || $t("common.empty") }}</p>
+  </div>
+</template>
+
+<style scoped>
+.empty {
+  padding: 60px 0;
+  text-align: center;
+  color: var(--mall-faint);
+}
+.icon {
+  font-size: 40px;
+  margin-bottom: 10px;
+}
+</style>