In the sprawling, mountainous city of Chongqing, where the Yangtze and Jialing rivers converge and the air hums with the energy of one of China’s most vibrant metropolises, a single dish has become a legend. This is Shuǐ Zhǔ Yú (水煮鱼), or “Boiled Fish.” But don’t let the simple name fool you. This is…