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/hooks.py

@@ -9,6 +9,13 @@ from core.registry import (
 def register() -> None:
     register_feature("shop")
     register_public_nav(section="shop", label="Shop", url_name="shop:list", order=30)
+    register_portal_nav(
+        section="shop_sales",
+        label="Sales",
+        url_name="shop_portal:sales",
+        group="Retail",
+        order=5,
+    )
     register_portal_nav(
         section="shop_products",
         label="Products",
@@ -28,7 +35,9 @@ def register() -> None:
 
 def _dashboard(request) -> dict:
     from shop.models import Order, Product
+    from shop.stats import sales_summary
 
+    sales = sales_summary()
     return {
         "open_shop_orders": Order.objects.filter(
             status__in=[Order.Status.OPEN, Order.Status.PAID]
@@ -39,4 +48,6 @@ def _dashboard(request) -> dict:
             fulfillment=Product.Fulfillment.STOCKED,
             stock_qty__lte=3,
         ).count(),
+        "shop_sales_30d": sales["order_count"],
+        "shop_revenue_30d": sales["revenue"],
     }