Installs /usr/local/bin/git-askpass (uses zenity or qarma) and sets
core.askPass in /etc/gitconfig. Git now pops a GUI dialog for username/
password instead of trying to open /dev/tty, which fails in headless
contexts (scripts, Claude Code terminal).
Adds zenity to live desktop package lists for both niri and cinnamon profiles.
Propagated to: both live ISO builders and the installer postinstall.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>