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>

assets/js/forum-runtime.js

@@ -134,6 +134,21 @@
       syncHidden('post_status', status.dataset.forumStatus)
       return
     }
+    const hideType = event.target.closest('[data-forum-hide-type]')
+    if (hideType) {
+      root.querySelectorAll('[data-forum-hide-type]').forEach((item) => item.classList.toggle('active', item === hideType))
+      syncHidden('hide_type', hideType.dataset.forumHideType)
+      return
+    }
+    const topic = event.target.closest('[data-forum-topic],[data-forum-topic-none]')
+    if (topic) {
+      const name = topic.dataset.forumTopic || ''
+      root.querySelectorAll('[data-forum-topic],[data-forum-topic-none]').forEach((item) => item.classList.toggle('active', item === topic))
+      syncHidden('topics', name)
+      const label = root.querySelector('[name="topics"]')
+      if (label) label.lastChild.textContent = name || '话题'
+      return
+    }
     const pick = event.target.closest('[data-forum-cover-pick]')
     if (pick) {
       root.querySelector('[data-forum-cover-file]')?.click()