merge_task only flipped the worktree to Merged; it never transitioned the task
status. With allowWaitingForReview this left a merged task stuck in
WaitingForReview. Approve it to Done on a successful merge (a Done task is
already terminal). Mirrors the ApproveAndMergeAsync review flow.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>