- Add new desktop and iOS screenshots under assets/screenshots, named by screen, theme and form factor, and optimized with pngquant + oxipng
- Add feature graphics under assets/feature-graphics: Play Store feature graphic, README hero and mobile strip, and phone/desktop store shots
- Use them in the README, Flathub metainfo (plain screenshots) and F-Droid metadata (phone screenshots + featureGraphic)
- Replace the Steam library hero with one made from the new UI
- Remove the old desktop and mobile screenshots
