feat(admin): implement order and customer operations experience

Orders dashboard (real orders-today/pending/paid/cancelled/refunded/customers/returning-customers/average-order/recent-activity/system-alerts, computed from the full order book not just the current page); orders list gains density, saved column visibility, bulk status change/archive/delete/export/print alongside existing search+status filter+pagination, sticky table header; order detail gets a visual status workflow stepper in business language (Pending/Packing/Shipping/Completed, with Cancelled/Refunded as terminal states) and a reusable OrderTimelineComponent replacing the flat text log; added a derived Customers feature (list + profile detail: statistics/lifetime value/addresses/orders/activity/notes) built entirely by grouping existing AdminOrder records by email - no new backend, no invented gateway, since no customer entity existed. Added archive/restore/delete to the orders gateway (soft-delete pattern mirroring categories) and filled in the adminOrders/adminCustomers i18n namespaces, which previously didn't exist at all (every adminOrders.* label was rendering as a raw key).

src/app/features/admin/shell/admin-nav.model.ts

@@ -31,6 +31,7 @@ export const ADMIN_NAV_PRIMARY: AdminNavEntry[] = [
   { type: 'link', id: 'products', icon: 'pi-box', labelKey: 'adminShell.nav.products', path: ['products'] },
   { type: 'link', id: 'categories', icon: 'pi-tags', labelKey: 'adminShell.nav.categories', path: ['categories'] },
   { type: 'link', id: 'orders', icon: 'pi-shopping-cart', labelKey: 'adminShell.nav.orders', path: ['orders'] },
+  { type: 'link', id: 'customers', icon: 'pi-user', labelKey: 'adminShell.nav.customers', path: ['customers'] },
   { type: 'link', id: 'transactions', icon: 'pi-credit-card', labelKey: 'adminShell.nav.transactions', path: ['transactions'] },
   { type: 'link', id: 'reviews', icon: 'pi-star', labelKey: 'adminShell.nav.reviews', comingSoon: true },
   { type: 'link', id: 'reports', icon: 'pi-chart-bar', labelKey: 'adminShell.nav.reports', comingSoon: true },