SAN FRANCISCO — By the time Alexandria Ocasio-Cortez took the stage in San Francisco Tuesday night, an adoring crowd of 500 at her sold-out fundraiser — many wearing “Democratic Socialists of America” t-shirts and buttons — were ready for the next revolution to begin. “Are we ready to change California? Are we ready to really throw down in San Francisco?” yelled the 28-year-old political wunderkind, fresh off a New York House primary upset, to cheers from the millennial-dominated audience.