Brian Armstrong, chief executive officer of Coinbase Global Inc., speaks during the Messari Mainnet summit in New York, on Thursday, Sept. 21, 2023.Michael Nagle | Bloomberg | Getty ImagesCoinbase is making its biggest push yet to reposition itself as a mainstream trading and financial platform, moving beyond crypto and into the broader retail investing stack as competitors show there's real money in always-on engagement products.The digital asset exchange announced Wednesday that it's rolling o...