Resume a schedule

Returns a paused schedule to active and re-arms its original planned instant. When that instant passed during the pause, the schedule's lateness policy applies exactly as it does after an outage: catchUp makes an occurrence inside its window due, while skipAhead or an expired window settles it skipped_stale. An occurrence already on its retry ladder is exempt from this first-arrival decision. Resuming an already active schedule changes nothing and returns the same version.