Zohran Mamdani’s “city-run groceries” gambit was always mostly symbolic — even he doesn’t pretend one-store-per-borough will be more than proof of concept — but it’s fast becoming a symbol and sign of how hollow his whole mayoralty could prove. Last week he at long last unveiled the plan for the first store: He says it will cost $30 million and take nearly three years to build . That’s 40% of what the mayor had said five groceries would cost — and many times what the private sector spends to