Removes one or more tags from a contact by UUID. Either tag_id (single tag) or tag_ids (comma-separated list) must be provided. 'removed' lists names of tags actually detached. 'skipped' lists UUIDs that either didn't resolve to a tag in this account or resolved but were not currently attached to the contact -- both cases mean the tag was not removed (because it wasn't there to begin with). The legacy singular path /contacts/delete_tag also accepts the same payload as an undocumented alias.