STOCKTON, Calif. — GILBERT MELENDEZ, NATE Diaz’s longtime teammate, was in Stockton with some of his students from El Niño Training Center in South San Francisco for a night training session at Nick Diaz Academy on Aug. 24. Melendez and crew arrived first at the “Trap House” — the name given by Nate Diaz to a small, two-bedroom guest house across from his property — where they chatted with Diaz’s team and watched YouTube videos on the big…