Notify online firm members in-game when a staff member is promoted or demoted.
Built on the firm notification system (PAR-94).
Technical notes — StaffCommands.promote / demote → FirmStaffService.promoteEmployee / demoteEmployee (already returns the new role name). After the role change, notifyFirm(firmId, "business.notify.employee.promoted"/"…demoted", "player", name, "role", newRole). The target and actor already receive direct messages today; this adds the firm-wide visibility.