Smaller downloads that Rufus/balenaEtcher/RPi-Imager still read directly (zstd
would break Windows flashers). Switches the image artifact, flashing commands
(xz -dc | dd, xz -t, unxz), publish flow (xz -T0 -c), the artifact-manifest
script, and all skills + docs to .img.xz. Adds a Windows (Rufus/Etcher) flashing
section + README pointer. Source tarballs (clawdie-ai *.tar.gz) unchanged.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
