SEOUL—North Korean leader Kim Jong Un’s wife, Ri Sol Ju, has been shown by state media appearing in public for the first time in more than a year, joining her husband at a concert on one of the country’s biggest holidays. North Korea’s state-run television channel on Thursday aired footage of the pair at the event marking the birthday of Kim’s late father and former leader Kim Jong Il. The official ruling Worker’s Party newspaper Rodong Sinmun had released photos of the pair at the event on Wednesday. Ri had often accompanied Kim to major public events, but had not been seen since January last year at an event for the Lunar New Year holiday, stoking speculation over her health and potential pregnancy. South Korea’s National Intelligence Service (NIS) told lawmakers on Tuesday that Ri appeared to have refrained from outside activities to head off coronavirus infections but was “playing …