KISMAYO, Somalia — Al Shabaab lost control of this port city late last month, its Al Qaeda-aligned fighters either fleeing into the countryside or melting into a wary population of civilians. A coalition of Somali and Kenyan soldiers are, for now, maintaining an armed peace. But basic services — like education, sanitation and health — are in ruins and aid agencies are, so far, mostly unwilling to take a chance on the city’s precarious security. Dr. Omar Saleh is the exception.