925a53e0f7
pin_version sets pin_kind='manual' and pin_label on the target row. Accepts already-pinned rows (promotes auto→manual, updates label). Labels are capped at PIN_LABEL_MAX_LEN=500 chars; longer values raise ValueError before any DB access. unpin_version clears both fields, downgrading the row to rolling. Does NOT delete — if the row is past the rolling FIFO depth, the next autosave's prune will drop it.