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/plugs/broken_url_tracker.ex

@@ -18,7 +18,7 @@ defmodule BerrypodWeb.Plugs.BrokenUrlTracker do
   def call(conn, {router, router_opts}) do
     router.call(conn, router_opts)
   rescue
-    e in Phoenix.Router.NoRouteError ->
+    e in [Phoenix.Router.NoRouteError, BerrypodWeb.NotFoundError] ->
       unless static_path?(conn.request_path) do
         prior_hits = Berrypod.Analytics.count_pageviews_for_path(conn.request_path)
         Berrypod.Redirects.record_broken_url(conn.request_path, prior_hits)