feat(links): align the friends page layout and submit UI

- assemble the friends template with page header, search cover, content position, widget zones and comments
- render the three page title styles and the tabbed search cover
- restore card, category nav and submit modal markup for the friends page
- add page content style support to the page editor
- port the linked card, category nav and submit modal styles to the mobile and desktop breakpoints

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/Frontend/PageAdminSet.php

@@ -242,6 +242,10 @@ class PageAdminSet {
 				$style = sanitize_key((string) wp_unslash($_POST['page_header_style']));
 				update_post_meta($post_id, 'page_header_style', in_array($style, ['', 'not', '1', '2', '3'], true) ? $style : '');
 			}
+			if (isset($_POST['page_content_style'])) {
+				$content_style = sanitize_key((string) wp_unslash($_POST['page_content_style']));
+				update_post_meta($post_id, 'page_content_style', in_array($content_style, ['', 'not', 'nobox', 'full'], true) ? $content_style : '');
+			}
 
 			$register = isset($_POST['widgets_register']) && $_POST['widgets_register'] === '1';
 			update_post_meta($post_id, 'widgets_register', $register ? '1' : '');
@@ -382,6 +386,18 @@ class PageAdminSet {
 						'3'    => __('封面图样式', 'jio'),
 					],
 				];
+				$inputs[] = [
+					'name'    => __('内容样式', 'jio'),
+					'id'      => 'page_content_style',
+					'std'     => (string) get_post_meta($post_id, 'page_content_style', true),
+					'type'    => 'radio',
+					'options' => [
+						''      => __('默认', 'jio'),
+						'not'   => __('不显示', 'jio'),
+						'nobox' => __('无背景', 'jio'),
+						'full'  => __('全屏无背景', 'jio'),
+					],
+				];
 				$inputs[] = [
 					'name'    => __('模块布局', 'jio'),
 					'id'      => 'widgets_register',