Soprano Lucy Shelton has premiered more than 100 new works in a decades-long career as a concert and recital artist. “I haven’t spent my time as an opera singer,” Shelton, 80, explained in a video chat last month. “I preferred vocal chamber music, and mostly new music where I worked with living composers.” But this week, Shelton will do something she has only done once before in her long, decorated career: premiere an opera. She stars in Lucidity by composer Laura Kaminsky and librettist David Cote, in a debut production presented by On Site Opera that opens tonight and runs through Saturday at New York City’s Abrons Arts Center.