Narrow scheduled backstop for stale Braintree renewal windows.

Scans active Braintree subscriptions whose current_period_end is past a grace window and which still have no local metered-renewal anchor for that closed period. Each stale row is repaired by reusing Accrue.Billing.MeteredRenewalActions.open_braintree_renewal_window/4 instead of inventing a scheduler-only billing path.