Mayor Zohran Mamdani didn’t show up to the Real Estate Board of New York’s spectacular 130th annual bash at the Waldorf-Astoria on Thursday. (No doubt he was consumed with the fine points of organizing snowplows .)  But a jubilant Gov. Kathy Hochul was there, exhorting the 1,100 movers and shakers to “Build, baby build” — drawing robust cheers from dealmakers who seemed oblivious to the new mayor’s snub. The REBNY bash looked, sounded and tasted like a celebration, notwithstanding political and