Tag, move, unsubscribe, or delete many contacts at once

Apply one action to up to 10,000 contacts: the IDs in contact_ids, or every contact matching filter (the same filters as GET /contacts). Actions: tag and untag (with tags), add_to_list and remove_from_list (with list_id), unsubscribe, and delete. Adding to a list mirrors each contact's status, so nobody is resubscribed. delete is permanent and requires confirm_count equal to the number of contacts it would delete; without it the API returns 409 with that count. IDs from another workspace are ignored.