Add shop, POS sync, event ticketing, and shipping catalog apps.

Clients can run in-house retail without Shopify while keeping the same
Docker/Django/Postgres stack and data-ownership promise. Closes #5.

site/shipping/hooks.py

@@ -0,0 +1,31 @@
+from core.registry import (
+    register_dashboard_collector,
+    register_feature,
+    register_portal_nav,
+)
+
+
+def register() -> None:
+    register_feature("shipping")
+    register_portal_nav(
+        section="shipping",
+        label="Shipping",
+        url_name="shipping:shipment_list",
+        group="Retail",
+        order=50,
+    )
+    register_dashboard_collector(_dashboard)
+
+
+def _dashboard(request) -> dict:
+    from shipping.models import Shipment
+    from shop.models import Order
+
+    labeled = Shipment.objects.filter(status=Shipment.Status.LABELED).values_list(
+        "order_id", flat=True
+    )
+    return {
+        "unshipped_orders": Order.objects.filter(status=Order.Status.PAID)
+        .exclude(pk__in=labeled)
+        .count()
+    }