SEOUL — Kim Seo-jeong, 17, a high school student, was wearing the traditional Chinese dress known as a qipao, holding a folding fan, and her friend was dressed as a maid as they joined a Halloween crowd in Itaewon, a popular nightlife district in central Seoul, on Saturday evening. They were excited to be there, having missed previous Halloween festivities because of the pandemic. But what was expected to be an enjoyable evening out soon turned into a nightmare, as thousands of people cramming into a narrow, hilly alley next to the Hamilton Hotel created a deadly crowd crush. Nearly...