Every Friday after school, dressed in their new South Korean prep-school uniforms — sweater vests, knee-highs, pleated skirts, and blazers — seventeen-year old Alice Choy and her little sister, Olivia, head to Myeongdong, brave a dank, basement-level stairwell full of graffiti, and slip into a noreabang. Back in San Francisco, when she still had friends…