Track the forum topic currently being processed on IngestionRun
(currentTopicId + currentAccountChannelMapId; additive migration) and
expose it on the live status. processArchiveSets gains an optional
shouldStop callback polled before each archive set; the forum branch
passes a live isTopicFetchEnabled check, so disabling a topic mid-run
lets the in-flight file finish, then skips the rest of that topic.
A new disableActiveTopic server action sets the topic's fetchEnabled
false (upsert), and the worker status panel shows a "Skip & disable
this topic" button while a topic is being processed. Future runs skip
the topic via the existing live per-topic read.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>