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/shop/portal_urls.py

@@ -0,0 +1,19 @@
+from django.urls import path
+
+from shop import views
+
+app_name = "shop_portal"
+
+urlpatterns = [
+    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"),
+    path(
+        "products/<uuid:pk>/stock/",
+        views.portal_stock_adjust,
+        name="product_stock",
+    ),
+    path("orders/", views.portal_order_list, name="order_list"),
+    path("orders/<uuid:pk>/", views.portal_order_detail, name="order_detail"),
+    path("webhooks/stripe/", views.stripe_webhook, name="stripe_webhook"),
+]