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/customers/models/admin-customer.model.ts

@@ -0,0 +1,19 @@
+import { AdminOrder } from '../../orders/models/admin-order.model';
+
+/**
+ * A customer is not its own stored entity - it's derived by grouping existing
+ * AdminOrder records by customer.email, since no customer gateway/backend exists.
+ * Every field here is a real aggregate over that customer's orders, never fabricated.
+ */
+export interface AdminCustomer {
+  email: string;
+  name: string;
+  phone: string;
+  orderCount: number;
+  totalSpent: number;
+  currency: string;
+  firstOrderAt: string;
+  lastOrderAt: string;
+  addresses: string[];
+  orders: AdminOrder[];
+}