Nuggets General Manager Masai Ujiri was named the N.B.A.’s executive of the year a day after the Nuggets’ George Karl won the coach of the year award. Ujiri, the first African-born general manager in a major American sport, helped build a team that won a franchise-record 57 games and went an N.B.A.-best 38-3 at home before being ousted in the first round of the playoffs by the Warriors.