SEOUL – Just weeks ago, South Korea was celebrating its hard-won gains against the coronavirus, easing social distancing, reopening schools and promoting a tech-driven anti-virus campaign President Moon Jae-in has called “K-quarantine.”But a resurgence of infections in the Seoul region where half of South Korea’s 51 million people live is threatening the country’s success story and prompting health authorities to warn that action must be taken now to stop a second wave.South Korea’s Centers for Disease Control and Prevention on Thursday reported 45 fresh cases of infection, a daily rise that has been fairly consistent since late May.