BEIJING — The body camera hung from the top of the IV drip, recording the slightest twitch made by Yang Guoliang as he lay bloody and paralyzed in a hospital bed after a police beating with bricks. By then, surveillance was nothing new for the Yang family in rural China, snared in an intricate network based on U.S. technology that spies on them and predicts what they’ll do. Their train tickets, hotel bookings, purchases, text messages and phone calls are forwarded to the government. Their house