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>

docs/BACKEND.md

@@ -168,6 +168,14 @@ Plus, if authenticated history/wishlist/compare/saved-searches sync is wanted: `
 
 **Frontend files:** implement `AdminMonitoringApiGateway`-equivalent methods against a to-be-defined `AdminMonitoringGateway` interface (`AdminMonitoringLocalGateway` currently has no interface extracted — add one when a real implementation is built, mirroring the pattern used everywhere else in `admin/*`).
 
+## 16. Analytics - visitors/funnels/heatmaps (Sprint 27, no backend at all)
+
+**Current behavior:** `features/admin/analytics/` computes real revenue/orders/top-products aggregations from the existing mock order data (see item 7), but visitor traffic, conversion funnels, and heatmaps have zero data source anywhere in this system (no analytics/tracking pipeline, no event collection) — these render `pending-backend` badges rather than fabricated numbers.
+
+**Needed:** a traffic/event tracking pipeline (page views, sessions, conversion events) and a funnel/heatmap aggregation service, before this section of the Analytics page can show anything real.
+
+**Frontend files:** `features/admin/analytics/pages/admin-analytics-page.component.html` currently renders the pending-backend badge inline (no gateway method exists for this yet, unlike every other mocked domain in this doc).
+
 ## Known reliability issues
 
 ### Production 502/504 Bad Gateway on refresh / back-navigation