Katie Couric celebrated her five years at CBS by partying like a rock star at 1Oak until 4 a.m. Friday. Still dressed in a blue power suit, she strolled into the Chelsea club at around 2 a.m. with a group of friends and co-workers hours after her final “Evening News” broadcast. They ordered two bottles of Veuve Clicquot and tons of beer. Couric was dancing on banquettes while DJ Jus Ske spun hip-hop. After the broadcast, Couric, who’s finalizing a deal with ABC, was toasted with speeches by Jeff Fager and David Rhodes. She headed to dinner and to a karaoke bar, where she sang “Build Me Up Buttercup” before hitting 1Oak.