Credit...Chang W. Lee and Michelle V. Agins/The New York Times; Ben Solomon for The New York Times It all began with the slightest of hand gestures by a coach in Serena Williams’s box and ended in chaos, recrimination and, oh, yes, Naomi Osaka’s remarkable upset victory. Here’s a breakdown of what happened in the women’s final of the 2018 United States Open: A Dream Matchup Osaka, a shy, 20-year-o