Jada Pinkett Smith stunned at her first appearance since the Oscars on Saturday, sporting a show-stealing strapless, glittering gold gown at the opening of the Rhimes Performing Arts Center and the Debbie Allen Dance Academy. It was her first time out since a post-Oscars party, after husband Will Smith strode up onstage to slap festivities host Chris Rock for a barb aimed at Smith’s wife. Rock made a Pinkett Smith-directed jab at her shaven head, wrapped in a joke about a sequel to “G.I. Jane,” in which the protagonist played by Demi Moore shaves her head. Pinkett Smith’s hair loss is not volu…