BEIJING — The hospital in southern Beijing advertised itself as specializing in vascular tumors, especially benign birthmarks that often appear in infants. But when a fire broke out there last month, killing at least 29 people, many of the victims had been there for another reason: They were older people with disabilities receiving nursing care, some of them staying at the private hospital for months or even years, even though it was not licensed as a provider of long-term elder care. The tragedy at Changfeng Hospital — the deadliest fire…