longbridge/gpui-kit ? reverse-engineered prompt

Build me a polished Rust desktop UI kit for cross platform apps, with a clean modern look and a lot of ready to use components like buttons, forms, menus, dialogs, tables, lists, tabs, layouts, and rich text display. I want it to feel fast and native on macOS, Windows, and Linux, with good keyboard support and accessibility built in.

Please also include a nice demo app or component gallery so I can see everything working, plus a couple of realistic screens like a data table view, a settings page, and a docked panel layout. If it makes sense, add theming so the styles can be customized without rewriting everything, and make sure the examples are easy to run. Look up current docs online if you need to, and keep the code organized so it is easy to extend later.