New York City is locking up more teenagers and keeping them longer behind bars, according to an early report card of Mayor Eric Adams’ second full year in office. The number of young people held every day in the city’s youth facilities surged 31% over the past year to, on average, 260 detainees, last week’s preliminary Mayor’s Management Report showed. The city is also on track to admit more teens to juvenile detention this year. “It’s much of a stain on New York City,” said Messiah Ramkissoon, associate executive director for strategic planning and community partnerships at Youth Justice Netw…