The city and 10 hospitals, including Johns Hopkins Hospital and University of Maryland Medical Center, are partnering to provide housing and services for 200 people and families, a program they hope will be a model for ending homelessness. The aim of the two-year pilot effort is to show that its “wraparound” treatment keeps people healthy, productive and in permanent homes. Leaders also hope to show the program is sustainable because they say it will reduce health-care spending over time.