Hooks the topology_worker's post-terminal path into a new
notify_run_completed repo helper that atomically transitions the topic
processing → reviewing when the completed run has research_topic_id set
AND no siblings for that topic are still queued or running. Guarded on
status='processing' so a retry, a re-fire, or a topic already past
processing are all no-ops. Best-effort at the worker; DB hiccups are
logged and never fail the run.
The manual /submit-review endpoint stays as an escape hatch for topics
that end up parked in processing with nothing to complete (updated the
doc comment).
