Photos by Katharine Shilcutt​In the heat of battle last night, the oysters -- and the chefs -- kept their cool. The fourth such event organized by Jenny Wang and the Houston Chowhounds, the Bivalve Throwdown at Stella Sola on Sunday afternoon saw 11 of the city's best chefs compete to create the best oyster dishes for a panel of distinguished judges. But that's where the "distinguished" part of the event ended: The afternoon was a celebration of the first Gulf oysters of the season that