Bootstrap installer that downloads the pre-patched XUI 1.5.13 package
from our Gitea generic-package mirror (GitHub fallback), checksum-verifies
it, and runs the bundled ./install. Includes preflight checks (root,
Ubuntu 20/22/24, x86_64, RAM/disk, re-install guard).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
