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>

test/support/conn_case.ex

@@ -32,9 +32,23 @@ defmodule BerrypodWeb.ConnCase do
   end
 
   setup tags do
-    Berrypod.DataCase.setup_sandbox(tags)
+    pid = Berrypod.DataCase.setup_sandbox(tags)
     Berrypod.Settings.SettingsCache.invalidate_all()
-    {:ok, conn: Phoenix.ConnTest.build_conn()}
+    # Clear caches without re-warming from DB (which would bypass sandbox)
+    BerrypodWeb.R.clear()
+    Berrypod.Pages.PageCache.invalidate_all()
+    Berrypod.Redirects.clear_cache()
+
+    # Add sandbox metadata to conn so Phoenix.Ecto.SQL.Sandbox plug
+    # can allow LiveView processes to access the test's DB connection
+    metadata = Phoenix.Ecto.SQL.Sandbox.metadata_for(Berrypod.Repo, pid)
+    encoded_metadata = Phoenix.Ecto.SQL.Sandbox.encode_metadata(metadata)
+
+    conn =
+      Phoenix.ConnTest.build_conn()
+      |> Plug.Conn.put_req_header("user-agent", encoded_metadata)
+
+    {:ok, conn: conn}
   end
 
   @doc """