Meta Platforms Inc.’s Mark Zuckerberg, months into building one of the priciest teams in technology history, is getting personally involved in day-to-day work and pivoting the company’s focus to an artificial intelligence model it can make money off of. One new model, codenamed Avocado, is expected to debut sometime next spring, and may be launched as a “closed” model — one that can be tightly controlled and that Meta can sell access to, according to people familiar with the matter, who declined...