feat(attachment): 按参考主题重构后台上传配置套件

- 新增 AKSRT\Attachment\UploadLimits：按用户类型解析图片/视频/文件
  上传上限（取最大值+默认兜底，钳制到 PHP 上限）、允许/禁止格式过滤、
  上传自动重命名、非管理员附件页 404；不含论坛角色
- 后台「附件配置」重做：大小限制/格式限制/上传行为三组配置，
  PHP Schema 与 SPA Schema 逐字段镜像（v1.2.0）
- 定制页 AttachmentPermissions.vue 改为标准 schemaPage，清理失效的
  API 包装、组件加载器与旧配置键（submit_image_max_size 等）
- 投稿/评论上传、批量上传数量全部切换到新链路；AksField 数字组件
  支持单位展示
- 更新 captcha harness 与 front-submit 契约测试；421 项测试通过

templates/pages/page-submit.php

@@ -81,9 +81,12 @@ if (file_exists($js)) {
 		(string) filemtime($js),
 		true
 	);
-	$submit_image_max_size = \AKSRT\Core\FrontSubmit::upload_limit_bytes('image');
-	$submit_video_max_size = \AKSRT\Core\FrontSubmit::upload_limit_bytes('video');
-	$resource_max_size = \AKSRT\Core\FrontSubmit::upload_limit_bytes('resource');
+	$upload_image_max_bytes = \AKSRT\Core\FrontSubmit::upload_limit_bytes('image');
+	$upload_video_max_bytes = \AKSRT\Core\FrontSubmit::upload_limit_bytes('video');
+	$upload_resource_max_bytes = \AKSRT\Core\FrontSubmit::upload_limit_bytes('resource');
+	$image_upload_multiple = class_exists('\AKSRT\Attachment\UploadLimits')
+		? \AKSRT\Attachment\UploadLimits::image_batch_limit()
+		: 6;
 
 	wp_localize_script('aksrt-front-submit-editor', 'aksrtSubmitData', [
 		'ajaxUrl'   => admin_url('admin-ajax.php'),
@@ -101,6 +104,7 @@ if (file_exists($js)) {
 
 
 		'leaveWarning' => !empty($ctx['settings']['leave_warning']),
+		'imageUploadMultiple' => $image_upload_multiple,
 		'ai'        => [
 			'available' => !empty($ctx['ai_available']),
 			'summary'   => !empty($ctx['ai_available']),
@@ -117,15 +121,15 @@ if (file_exists($js)) {
 		'uploads'   => [
 			'image' => !empty($ctx['can_upload_img']) ? [
 				'url'     => esc_url_raw(rest_url('aksrt/v1/front-submit/upload/image')),
-				'maxSize' => $submit_image_max_size,
+				'maxSize' => $upload_image_max_bytes,
 			] : null,
 			'video' => !empty($ctx['can_upload_video']) ? [
 				'url'     => esc_url_raw(rest_url('aksrt/v1/front-submit/upload/video')),
-				'maxSize' => $submit_video_max_size,
+				'maxSize' => $upload_video_max_bytes,
 			] : null,
 			'resource' => !empty($ctx['can_upload_file']) ? [
 				'url'     => esc_url_raw(rest_url('aksrt/v1/front-submit/upload/resource')),
-				'maxSize' => $resource_max_size,
+				'maxSize' => $upload_resource_max_bytes,
 			] : null,
 		],
 		'i18n'      => [