Resume a paused job.

For cron jobs the next fire is computed from now(). For every jobs the next fire is the next epoch grid boundary of the interval — (floor(now / intervalMs) + 1) * intervalMs — NOT a full interval after now(): grid alignment is what makes replicas started at different instants agree on fire times and distributed-lock slot keys (M70l X10-2). Breaking vs 0.1.0-alpha.8: the released contract stated the interval "restarts from now"; the fire may now come sooner than one full interval after resume (never later). For delay jobs the full original delayMs is re-armed from now().

Idempotent — calling resume on a running job is a no-op.