Robinhood CEO Vlad Tenev has a lot to celebrate this holiday season. After a bumpy few years following Robinhood’s 2021 IPO — a period during which shares of the commission-free trading app plummeted by more than 90% after it abruptly restricted trading in some meme stocks —  the 12-year-old company was just declared Yahoo Finance’s “comeback stock” of the year. Asked about that accolade in recent days over Zoom, Tenev was beaming. “When we were a young company and just got started, everyone was...