Switch the text-login shell from zsh to brush now that brush builds and
packages for Redox. base.toml [users.root]/[users.user] -> /usr/bin/brush
covers mini (which inherits base); redbear-bare.toml gets the same shell
plus the brush package so bare and mini share an identical boot-to-login
path (bare stays the minimal boot-test surface, mini adds the app payload).
bare/full keep their own [users.root]; full and the greeter remain on zsh
(that is the graphical/sddm path, handled separately). zsh stays installed
as a fallback. Verified: redbear-mini.iso builds and its /etc/passwd reads
`.../usr/bin/brush` for root and user.
vasilito
c096e29825