Marketing screenshots

The screenshots in the README and on this site are generated, never taken by hand:

This starts a private Xvfb display of a fixed size, runs BiscuitTin with fictional config and settings, and drives it with a script of button presses. BiscuitTin saves each PNG from its own window (-script with shot steps), so images contain only the window, are always exactly the same size, and are pixel-identical between runs. The images, screenshots.ini, and the generated screenshot-manifest.yaml for indexers are in var/marketing/screenshots/.

You need Xvfb (dnf install xorg-x11-server-Xvfb) and network access for the tile icons.

See var/marketing/screenshots/README.md for how to add a screenshot, and the step format in desktop/internal/app/script.go. make docs copies the images into the site.