Add a shop sales dashboard with 30-day charts (#4)

## Summary
- Closes #3
- Portal Retail **Sales** page: 30-day orders/revenue/units/AOV, daily charts, top products
- Home dashboard cards for 30-day shop sales and revenue
- Stacks on #2. 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; unpaid/old excluded
- [ ] Home dashboard shows 30-day sales count
- [ ] `manage.py test shop`

Reviewed-on: #4

site/shop/views.py

@@ -34,6 +34,7 @@ from shop.services import (
     store_product_stl,
     sync_product_colors,
 )
+from shop.stats import sales_dashboard
 
 logger = logging.getLogger(__name__)
 
@@ -344,6 +345,11 @@ def portal_stock_adjust(request, pk):
     return redirect("shop_portal:product_edit", pk=product.pk)
 
 
+@login_required
+def portal_sales(request):
+    return render(request, "shop/portal/sales.html", sales_dashboard())
+
+
 @login_required
 def portal_order_list(request):
     orders = Order.objects.all()[:200]