feat(admin): analytics dashboard

Sprint 27.

New features/admin/analytics/ module + net-new /:lang/backoffice/analytics
route + Dashboard Quick Action.

- revenue/orders/avg-order-value/sales-over-time/top-products computed by
  composing AdminOrdersLocalGateway (Sprint 23's seeded mock orders) - real
  aggregation over mock data, not a separate fabricated dataset
- products/categories counts from AdminProductsLocalGateway/
  AdminCategoriesLocalGateway
- visitors/funnels/heatmaps render pending-backend badges (no analytics
  pipeline exists anywhere in this system) rather than fabricated numbers,
  same convention as the Sprint 19 dashboard's pre-Sprint-23 Orders/Revenue
  cards
- plain div-bar chart (no charting library), 7/30/90-day range toggle,
  CSV export

docs/ADMIN.md + docs/BACKEND.md (new item 16) updated.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/app/features/admin/analytics/models/admin-analytics.model.ts

@@ -0,0 +1,22 @@
+export type AdminAnalyticsDateRange = 7 | 30 | 90;
+
+export interface AdminAnalyticsSummary {
+  revenueTotal: number;
+  currency: string;
+  ordersCount: number;
+  avgOrderValue: number;
+  productsCount: number;
+  categoriesCount: number;
+}
+
+export interface AdminAnalyticsSeriesPoint {
+  date: string;
+  value: number;
+}
+
+export interface AdminAnalyticsTopProduct {
+  productId: string;
+  name: string;
+  quantity: number;
+  revenue: number;
+}