NEW YORK — President Joe Biden praised New York Mayor Eric Adams’ crime-fighting agenda Thursday and unveiled a new federal initiative aimed at stemming a flow of illegal weapons from southern states that has contributed to the city’s recent spike in violence. Marking his first visit to New York since Adams’ inauguration, Biden gave the mayor his seal of approval during a press conference at the NYPD’s downtown Manhattan headquarters, where they also received a classified briefing from the department’s joint gun violence task force. “I want to help every major city follow New York’s lead,” sai…