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>

assets/css/admin/components.css

@@ -2543,6 +2543,73 @@
   width: 5rem;
 }
 
+.page-settings-hint {
+  font-size: 0.6875rem;
+  color: var(--admin-text-secondary);
+  margin: 0;
+  padding-top: 0.125rem;
+}
+
+/* URL editor - segmented input for page URLs */
+
+.url-editor {
+  display: flex;
+  align-items: center;
+  gap: 0;
+}
+
+.url-editor-slash {
+  padding: 0.375rem 0.25rem;
+  background: var(--admin-bg);
+  border: 1px solid var(--admin-border);
+  border-right: none;
+  font-size: 0.875rem;
+  color: var(--admin-text-tertiary);
+
+  &:first-child {
+    border-radius: var(--admin-radius) 0 0 var(--admin-radius);
+  }
+}
+
+.url-editor-input {
+  border-radius: 0;
+  flex: 1;
+  min-width: 4rem;
+
+  &:last-child {
+    border-radius: 0 var(--admin-radius) var(--admin-radius) 0;
+  }
+}
+
+.url-editor-segmented .url-editor-input {
+  flex: 0 1 auto;
+  width: auto;
+}
+
+.url-editor-prefix {
+  max-width: 8rem;
+}
+
+.url-editor-fixed {
+  padding: 0.375rem 0.5rem;
+  background: var(--admin-bg);
+  border: 1px solid var(--admin-border);
+  border-left: none;
+  border-radius: 0 var(--admin-radius) var(--admin-radius) 0;
+  font-size: 0.875rem;
+  color: var(--admin-text-tertiary);
+  font-style: italic;
+}
+
+.url-editor-fixed-path {
+  padding: 0.375rem 0.5rem;
+  background: var(--admin-bg);
+  border: 1px solid var(--admin-border);
+  border-radius: var(--admin-radius);
+  font-size: 0.875rem;
+  color: var(--admin-text-secondary);
+}
+
 /* Block list in editor */
 
 .block-list {