fyne-io/fyne ? reverse-engineered prompt

Build me a simple cross platform app toolkit in Go that lets me make desktop and mobile apps from one codebase.

I want the basics to just work, like opening windows, showing text, buttons, menus, dialogs, forms, layouts, themes, images, clipboard, storage, notifications, and simple drawing on a canvas. It should feel easy for someone new to Go, with a small hello world app and a demo app that shows off the common widgets and light and dark themes.

Please make it run on desktop first, but keep it ready for mobile too, including Android and iOS support where possible. Add a clean README with getting started steps, a tiny example app, and notes on how to run the widget demo and package for mobile. If anything depends on current docs or platform setup, look it up online if you need to.