Sweden has given the world many wonderful gifts. Zara Larsson, obviously. Spotify and social democracy. And Ikea, the company that showed us you can furnish your apartment, stylishly and affordably, with the contents of a few flatpack boxes.  Sweden’s talent for mass-producing clever, easy-to-assemble home fixtures also extends to something much bigger than bookshelves and bed frames: building entire houses and apartments. Ikea has become one of the biggest furniture retailers in the US (and perhaps our top purveyor of vegan meatballs). But those factory-built Swedish homes? American...