feat(forum): add quick publish, captcha and hidden content

Port the reference inline quick-publish composer to the forum home:
title/body inputs, image upload, plate/topic/access/hidden-content
dropdowns and save/publish actions. Wire the site captcha into forum
publishing through a new `forum_post` scene (admin + REST gate), and
turn the hidden-content box into the theme's own visibility shortcodes
(login/comment/vip/payshow) so the existing gate renderer unlocks them.

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

inc/modules/captcha.php

@@ -374,6 +374,7 @@ function jio_captcha_scenes(): array {
 		'download'          => __('资源下载', 'jio'),
 		'signin'            => __('每日签到', 'jio'),
 		'front_submit'      => __('前台投稿', 'jio'),
+		'forum_post'        => __('论坛发帖', 'jio'),
 		'tip_user'          => __('打赏用户', 'jio'),
 		'ticket_create'     => __('提交工单', 'jio'),
 		'ticket_reply'      => __('回复工单', 'jio'),