When California voters broadly legalized marijuana, they were promised that a vast computer platform would closely monitor products moving through the new market. But 16 months after sales kicked in, the system known as track-and-trace isn’t doing much of either.    As of last month, just nine retail outlets were entering data into the network established under an estimated $60 million state contract, even though 627 shops are licensed to sell pot in California. The rate of participation is similarly slim for other sectors in the emerging industry.