The Nigerian singer won a Grammy and worked for Beyoncé, Drake and Rihanna before making her first album. Now it’s time to be her own boss. Openiyi, better known as Tems, had stopped on the East Coast on her way to Los Angeles, where she would soon begin rehearsals for her debut appearance at the Coachella music festival. It would be one in a swiftly multiplying series of firsts for the singer, songwriter and producer, whose music slides between R&B, pop and Afrobeats: her first album, “Born in the Wild,” due June 7 from RCA; its first single, the blissful party starter “Love Me JeJe”; her first headlining world tour, kicking off June 11. As far as milestones are concerned, a first earthquake was just another line in the tally.