Sixty-six “poor urban settlements” — some small, some enormous — bump against Nairobi’s sleek, downtown skyline like moths circling a light bulb. Kibera, a 6-kilometer-long expanse of tin-roofed shacks following the railway, is home to 1 million people — one of the largest slums in the world. Mathare counts at least 500,000 people. Dandora surrounds a city dump that stretches…