feat(messages): redesign native message admin page

- Rebuild users.php?page=aksrt_messages: overview stats, collapsible
  compose card (users list / role recipients), read-state views,
  type/recipient/keyword filters, bulk mark-read/delete, shared
  AdminListPagination
- Extract NotificationAdminQuery / AdminBroadcast / MessageTypes under
  src/Messages; page logic lives in UsersMenusMessages trait
- Page-scoped assets/css/admin/messages.css
- Remove dead aksrt_notification_type_label() and
  Message::get_all_notifications()

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

inc/modules/user-notifications.php

@@ -50,25 +50,6 @@ function aksrt_get_user_notifications(int $user_id = 0): array {
 }
 endif;
 
-if (!function_exists('aksrt_notification_type_label')) :
-/** 通知类型中文标签 */
-function aksrt_notification_type_label(string $type): string {
-    $map = [
-        'comment_reply'     => __('评论回复', 'aksrt'),
-        'comment_approved'  => __('评论审核', 'aksrt'),
-		'comment'           => __('文章评论', 'aksrt'),
-        'download_ready'    => __('下载就绪', 'aksrt'),
-		'post_favorite'    => __('文章收藏', 'aksrt'),
-		'post_like'        => __('文章点赞', 'aksrt'),
-		'comment_like'     => __('评论点赞', 'aksrt'),
-		'followed'         => __('新增关注', 'aksrt'),
-        'pending_comments'  => __('待审核评论', 'aksrt'),
-        'notice'            => __('通知', 'aksrt'),
-    ];
-    return $map[$type] ?? $type;
-}
-endif;
-
 if (!function_exists('aksrt_get_user_notification_count')) :
 /** 获取用户提醒总数 */
 function aksrt_get_user_notification_count(int $user_id = 0): int {