NEW YORK — For nearly seven weeks, Melora Hardin is trading the offices of Scranton's Dunder Mifflin for the bright lights of Broadway. The actress who plays Jan Levenson on the hit NBC TV series "The Office" will join the cast of "Chicago" Dec. 29 to portray that killer chorine Roxie Hart. Hardin will appear in the long-running revival at the Ambassador Theatre through Feb. 12. "I'm…