LOS ANGELES — A jury found Meta and YouTube negligent in the design or operation of their social media platforms, producing a bellwether verdict in the first lawsuit to take tech giants to trial for social media addiction. The Los Angeles County Superior Court jury said that Meta's and YouTube's negligence were a substantial factor in causing harm to the plaintiff, identified in court by her initials, K.G.M., and that the companies failed to adequately warn users of the dangers of Instagram (Meta's platform) and YouTube (which is owned by Google). It awarded K.G.M. $3 million in compensatory damages, finding Meta 70% responsible for harm caused to the now 20-year-old plaintiff, and YouTube responsible for 30%.…