ListForumTopics / GetForumTopicsByID / GeneralForumTopic gated on
membership while channel history uses the public-preview path, so a
public forum's topics (General included) were invisible until you joined.
Switch them to getChannelForViewer / channelForViewerLocked; private
forums and write paths keep the membership gate.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
