Locked NXT identifier settings and review workflow

For GiveCampus integrations and API.

The redesigned NXT settings display Lookup ID when no saved type exists, but preserve an explicitly saved System ID. The control locks after an external import has started. A gray/locked control is not proof that Lookup ID is saved: read its displayed value or ask Support to inspect it. Gifts to Review and Pending Export concern integration matching/errors for eligible gift/registration exports, not approval of donor payments or finalization of registrations. Their availability depends on enabled export workflows and permissions.