BENI, Congo — Faida Mwenge’s baby boy is nearly 3 months old but she and her son are still not allowed to leave the hospital — not until their bill is paid. The 20-year-old in eastern Congo has been detained since giving birth via an emergency cesarean section and owes hospital authorities $190 before she and little Jospin will be released. Mwenge is one of hundreds of thousands of people estimated to be illegally detained every year by hospitals in poor countries worldwide, according to a new study attempting to quantify the problem, which experts describe as a major violation of human rights.