feat(nav): finish remaining parity gaps (image_select, AJAX search, senior UI)

- Layout image_select previews (zibll PNGs under assets/images/header-layout)
- Localize aksrtAdminData.themeUri for admin SPA asset URLs
- Layout-2 inline search AJAX suggestions via aksrt_search_suggestions
- Appearance→Menus visual senior submenu editor (cards/columns)
- Acceptance checklist + automated source contract report

assets/admin/src/schema/sections/page-display/index.js

@@ -3,6 +3,14 @@
  * Each key corresponds to a sub-page under the "页面&显示" section.
  */
 
+/** Theme asset base for layout previews (admin SPA). */
+function themeAsset(path) {
+  const base = (typeof window !== 'undefined' && window.aksrtAdminData && window.aksrtAdminData.themeUri)
+    ? String(window.aksrtAdminData.themeUri).replace(/\/$/, '')
+    : ''
+  return base ? `${base}/${path.replace(/^\//, '')}` : path
+}
+
 /** Homepage sort options — keep in sync with AKSRT_Settings_Home_Cms::homepage_allowed_sorts() */
 const sortOptions = [
   { label: '最近更新', value: 'modified' },
@@ -79,23 +87,23 @@ export const pageDisplaySchemas = {
           {
             key: 'header_layout',
             label: '电脑端布局',
-            type: 'radio',
-            default: '2',
+            type: 'image_select',
+            default: '1',
             options: [
-              { label: '布局 1（经典）', value: '1' },
-              { label: '布局 2（内联搜索）', value: '2' },
-              { label: '布局 3（紧凑）', value: '3' },
+              { label: '布局 1（经典）', value: '1', image: themeAsset('assets/images/header-layout/header_layout_1.png') },
+              { label: '布局 2（内联搜索）', value: '2', image: themeAsset('assets/images/header-layout/header_layout_2.png') },
+              { label: '布局 3（紧凑）', value: '3', image: themeAsset('assets/images/header-layout/header_layout_3.png') },
             ],
-            help: '不同布局切换导航 DOM 结构',
+            help: '不同布局切换导航 DOM 结构（与 zibll image_select 一致）',
           },
           {
             key: 'mobile_header_layout',
             label: '移动端布局',
-            type: 'radio',
+            type: 'image_select',
             default: 'center',
             options: [
-              { label: '居中（含搜索按钮）', value: 'center' },
-              { label: '靠左', value: 'left' },
+              { label: '居中（含搜索按钮）', value: 'center', image: themeAsset('assets/images/header-layout/mobile_header_layout_center.png') },
+              { label: '靠左', value: 'left', image: themeAsset('assets/images/header-layout/mobile_header_layout_left.png') },
             ],
           },
           {