JUPITER, Fla. — Trey Mancini last season watched what the Miami Marlins did from a distance. He saw a scrappy team with an underdog mentality push its way into the playoffs and defy the odds they were given. After being inside the clubhouse for one week of spring training, he has a better understanding of how they got to that point. “It’s such a close-knit team,” Mancini said. “It’s always great to come in into a situation like that.” Mancini is with the Marlins on a minor-league deal. The 31-year-old first baseman has a track record for being a professional hitter and can play solid defense b…