Preview recoverable stale-listing suspensions

Returns a dry-run view of stale paid third-party listings that would be recoverably suspended. This route is read-only: it does not suspend, refund, notify, audit, or otherwise mutate listings. Each candidate reports would_suspend: true, the estimated collateral refund, and recovery_state showing status: "paused" and review_status: "suspended"; the listing remains recoverable through re-review rather than being permanently rejected.