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/components/shop_components/cart.ex

@@ -6,6 +6,7 @@ defmodule BerrypodWeb.ShopComponents.Cart do
   import BerrypodWeb.ShopComponents.Base
 
   alias Berrypod.Products.{Product, ProductImage}
+  alias BerrypodWeb.R
 
   defp close_cart_drawer_js do
     Phoenix.LiveView.JS.push("close_cart_drawer")
@@ -193,7 +194,7 @@ defmodule BerrypodWeb.ShopComponents.Cart do
     >
       <%= if @mode != :preview do %>
         <.link
-          patch={"/products/#{@item.product_id}"}
+          patch={R.product(@item.product_id)}
           class={["cart-item-image", !@item.image && "cart-item-image--empty"]}
           data-size={if @size == :compact, do: "compact"}
           style={if @item.image, do: "background-image: url('#{@item.image}');"}
@@ -212,7 +213,7 @@ defmodule BerrypodWeb.ShopComponents.Cart do
         <h3 class="cart-item-name" data-size={if @size == :compact, do: "compact"}>
           <%= if @mode != :preview do %>
             <.link
-              patch={"/products/#{@item.product_id}"}
+              patch={R.product(@item.product_id)}
               class="cart-item-name-link"
             >
               {@item.name}
@@ -321,7 +322,7 @@ defmodule BerrypodWeb.ShopComponents.Cart do
         </button>
       <% else %>
         <.link
-          patch="/collections/all"
+          patch={R.collection("all")}
           class="cart-continue-link"
         >
           Continue shopping
@@ -533,7 +534,7 @@ defmodule BerrypodWeb.ShopComponents.Cart do
           </.shop_button>
           <p class="order-summary-notice">Checkout isn't available yet.</p>
           <.shop_link_outline
-            href="/collections/all"
+            href={R.collection("all")}
             class="order-summary-continue"
           >
             Continue shopping
@@ -544,7 +545,7 @@ defmodule BerrypodWeb.ShopComponents.Cart do
           </.shop_button>
           <p class="order-summary-notice">Remove unavailable items to checkout.</p>
           <.shop_link_outline
-            href="/collections/all"
+            href={R.collection("all")}
             class="order-summary-continue"
           >
             Continue shopping
@@ -557,7 +558,7 @@ defmodule BerrypodWeb.ShopComponents.Cart do
             </.shop_button>
           </form>
           <.shop_link_outline
-            href="/collections/all"
+            href={R.collection("all")}
             class="order-summary-continue"
           >
             Continue shopping