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/live/shop/pages/search.ex

@@ -7,6 +7,7 @@ defmodule BerrypodWeb.Shop.Pages.Search do
   import Phoenix.LiveView, only: [push_patch: 2]
 
   alias Berrypod.{Pages, Search}
+  alias BerrypodWeb.R
 
   def init(socket, _params, _uri) do
     page = Pages.get_page("search")
@@ -32,7 +33,7 @@ defmodule BerrypodWeb.Shop.Pages.Search do
   end
 
   def handle_event("search_submit", %{"q" => query}, socket) do
-    {:noreply, push_patch(socket, to: "/search?q=#{query}")}
+    {:noreply, push_patch(socket, to: R.search() <> "?q=#{query}")}
   end
 
   def handle_event(_event, _params, _socket), do: :cont