Ghost Kitchens Are Dying. Here's the $15 Billion Lesson Every Restaurateur Must Learn.A ghost kitchen stripped away everything you think makes a restaurant a restaurant. No dining room. No servers. No storefront. No customers walking through the door. Just a kitchen. Four walls. Commercial equipment. And a phone that never stops ringing with delivery orders.Ghost kitchens exist only in the digital world. Customers find them on DoorDash, Uber Eats, and Grubhub. They order through an app. Food get...