integrate R module and add url editor ui

Replaces hardcoded paths with R module throughout:
- Shop components: layout nav, cart, product links
- Controllers: cart, checkout, contact, seo, order lookup
- Shop pages: collection, product, search, checkout success, etc.
- Site context: nav item url resolution

Admin URL management:
- Settings page: prefix editor with validation feedback
- Page renderer: url_editor component for page URLs
- CSS for url editor styling

Test updates for cache isolation

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

lib/berrypod_web.ex

@@ -44,6 +44,8 @@ defmodule BerrypodWeb do
       use Gettext, backend: BerrypodWeb.Gettext
 
       import Plug.Conn
+      # Runtime URL paths (custom slugs/prefixes)
+      alias BerrypodWeb.R
 
       unquote(verified_routes())
     end
@@ -53,6 +55,11 @@ defmodule BerrypodWeb do
     quote do
       use Phoenix.LiveView
 
+      # Enable sandbox access for LiveView processes in test mode
+      if Application.compile_env(:berrypod, :env) == :test do
+        on_mount BerrypodWeb.LiveSandboxHook
+      end
+
       unquote(html_helpers())
     end
   end
@@ -93,6 +100,8 @@ defmodule BerrypodWeb do
       # Common modules used in templates
       alias Phoenix.LiveView.JS
       alias BerrypodWeb.Layouts
+      # Runtime URL paths (custom slugs/prefixes)
+      alias BerrypodWeb.R
 
       # Routes generation with the ~p sigil
       unquote(verified_routes())