fix(admin): improve native link manager filters

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

src/Admin/LinkManager.php

@@ -12,11 +12,56 @@ defined('ABSPATH') || exit;
 final class LinkManager {
 	public static function init(): void {
 		add_action('admin_bar_menu', [self::class, 'add_toolbar_node'], 999);
+		add_action('admin_enqueue_scripts', [self::class, 'enqueue_assets']);
 		add_filter('manage_link-manager_columns', [self::class, 'filter_columns']);
+		add_filter('get_terms_args', [self::class, 'show_empty_categories'], 10, 2);
+		add_filter('wp_dropdown_cats', [self::class, 'render_empty_category_option'], 10, 2);
 		add_action('manage_link_custom_column', [self::class, 'render_column'], 10, 2);
 		add_action('add_meta_boxes_link', [self::class, 'add_edit_help']);
 	}
 
+	public static function enqueue_assets(string $hook): void {
+		if ($hook !== 'link-manager.php') {
+			return;
+		}
+		$path = get_template_directory() . '/assets/css/admin/links-manager.css';
+		if (is_file($path)) {
+			wp_enqueue_style(
+				'jio-links-manager',
+				get_template_directory_uri() . '/assets/css/admin/links-manager.css',
+				[],
+				(string) filemtime($path)
+			);
+		}
+	}
+
+	/** Include empty link categories in the link-manager filter. */
+	public static function show_empty_categories(array $args, array $taxonomies): array {
+		if (self::is_link_manager_screen() && in_array('link_category', $taxonomies, true)) {
+			$args['hide_empty'] = false;
+		}
+		return $args;
+	}
+
+	/** Give the category filter a readable option when no categories exist. */
+	public static function render_empty_category_option(string $output, array $args): string {
+		if (!self::is_link_manager_screen()
+			|| ($args['taxonomy'] ?? '') !== 'link_category'
+			|| ($args['name'] ?? '') !== 'cat_id'
+			|| preg_match('/<option\\b/i', $output)
+		) {
+			return $output;
+		}
+
+		$placeholder = '<option value="" selected disabled>' . esc_html__('暂无链接分类', 'jio') . '</option>';
+		$updated = preg_replace('/(<select\\b[^>]*>)(\\s*)<\\/select>/i', '$1' . $placeholder . '</select>', $output, 1);
+		return is_string($updated) ? $updated : $output;
+	}
+
+	private static function is_link_manager_screen(): bool {
+		return is_admin() && ($GLOBALS['pagenow'] ?? '') === 'link-manager.php';
+	}
+
 	public static function add_toolbar_node(\WP_Admin_Bar $admin_bar): void {
 		if (!current_user_can('manage_links')) {
 			return;