Re-close an assigned customer's closed GL period in place after its ledger changed

For a closed month that changed after its close (#2835). Runs the same pre-close gate as the close route, brings the period's closing entry in line with its current profit and loss when it no longer matches, then moves closedAt to the database cutoff captured before review and closedByUserId to the caller. Changes after that cutoff keep the month-end closed_period_changed advisory for another review. The period stays closed throughout and no other period is touched, so it works for a month that has newer closed months after it. Writes an audit_logs entry (action reclose) with the supplied reason. The agent service API key may re-close a period as a high-impact operation with the same mandatory reason (2026-10-06, reversing #2411 for this route).