sync-worktrees

他の PR を main にマージした後、進行中の各 worktree に main を取り込む (merge) ワークフロー。並行している worktree が main から遅れるのを一括で 解消する。Trigger when the user says: "worktreeにmainを取り込む", "worktreeを最新化", "worktree同期", "mainを取り込む", "sync worktrees", "merge main into worktrees", "update worktrees with main", or similar phrases requesting to bring the default branch into in-flight worktrees.