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>