fix(token-usage): settle reconcile flags before the drain ack

handle_drain acknowledged the barrier before the deferred settle ran,
so `git-ai await` could report success while a correction from a
failed inline reconcile (or a deferred sweep settle the pending drain
had suppressed) was still pending. The settle now runs inside the
barrier, unthrottled like all barrier work, before the completion is
sent — normally a single SELECT — and the redundant post-drain settle
in the run loop is removed.

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