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/public_urls.py

@@ -0,0 +1,16 @@
+from django.urls import path
+
+from shop import views
+
+app_name = "shop"
+
+urlpatterns = [
+    path("", views.product_list, name="list"),
+    path("cart/", views.cart_view, name="cart"),
+    path("cart/add/<slug:slug>/", views.cart_add, name="cart_add"),
+    path("cart/update/<slug:slug>/", views.cart_update, name="cart_update"),
+    path("checkout/", views.checkout, name="checkout"),
+    path("checkout/<uuid:pk>/success/", views.checkout_success, name="checkout_success"),
+    path("checkout/<uuid:pk>/cancel/", views.checkout_cancel, name="checkout_cancel"),
+    path("<slug:slug>/", views.product_detail, name="detail"),
+]