Sergey Brin, president of Alphabet and co-founder of GoogleDavid Paul Morris | Bloomberg | Getty ImagesGoogle co-founder Sergey Brin, in a rare public appearance over the weekend, told a group of artificial intelligence enthusiasts that he came out of retirement "because the trajectory of AI is so exciting."Brin, 50, spoke to entrepreneurs on Saturday at the "AGI House" in Hillsborough, California, just south of San Francisco, where developers and founders were testing Google's Gemini model. AGI...