TikTok, the short-form video platform favored by young adults and teens, has launched a new feature that allows users to shop for products associated with a sponsored Hashtag Challenge, without leaving its app. These sponsored challenges are Gen Z-friendly marketing campaigns where users are prompted to post videos of them using a product — like showing off favorite outfits from Uniqlo or Guess, for example. Or they might participate in some sort of manufactured viral trend, like singing...