They work long hours, often to exhaustion. Many are paid by the piece — not garments, but blog posts. This is the digital-era sweatshop. You may know it by a different name: home. A growing work force of home-office laborers and entrepreneurs, armed with computers and smartphones and wired to the hilt, are toiling under great physical and emotional stress created by the around-the-clock Internet economy that demands a constant stream of news and comment.