Jeff Bezos is ramping up Amazon.com Inc. (AMZN)’s entertainment ambitions, buying video-game service Twitch Interactive Inc. in one of its biggest-ever acquisitions. Amazon said it’s paying $970 million in cash for the online gathering place for gamers. The deal, which trumped Google Inc.’s pursuit of the startup, is worth about $1.1 billion when including retention-related payouts, said a person familiar with the deal, who asked not to be identified because the talks are private.