Add a shop sales dashboard with 30-day charts (#8)

## Summary
- Closes #7
- Portal Retail **Sales** page: 30-day orders/revenue/units/AOV, daily charts, top products
- Home dashboard cards for 30-day shop sales and revenue when `FEATURE_SHOP` is on
- Stacks on #6 (shop catalog). Merge that first, then retarget `master` if needed.

## Test plan
- [ ] Sales page requires login; empty state with no paid orders
- [ ] Paid/fulfilled in the last 30 days counted; draft/open/cancelled/old excluded
- [ ] Top products ranked by units; home dashboard shows 30-day sales count
- [ ] `manage.py test shop core.tests_features`

Reviewed-on: #8

site/shop/portal_urls.py

@@ -5,6 +5,7 @@ from shop import views
 app_name = "shop_portal"
 
 urlpatterns = [
+    path("sales/", views.portal_sales, name="sales"),
     path("products/", views.portal_product_list, name="product_list"),
     path("products/new/", views.portal_product_edit, name="product_new"),
     path("products/<uuid:pk>/", views.portal_product_edit, name="product_edit"),