config: use brush as the login shell for bare and mini

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.

config/base.toml

@@ -296,12 +296,12 @@ symlink = true
 password = "password"
 uid = 0
 gid = 0
-shell = "/usr/bin/zsh"
+shell = "/usr/bin/brush"
 
 [users.user]
 # Password is unset
 password = ""
-shell = "/usr/bin/zsh"
+shell = "/usr/bin/brush"
 
 # Group settings
 [groups.sudo]

config/redbear-bare.toml

@@ -31,6 +31,7 @@ filesystem_size = 192
 ca-certificates = {}  # explicitly empty (overrides minimal)
 pkgutils = {}         # explicitly empty (overrides minimal)
 kibi = {}             # explicitly empty (overrides minimal)
+brush = {}            # login shell (bare matches mini up to login)
 
 # Override base.toml's network config — no DNS, no IP, no router
 [[files]]
@@ -147,11 +148,11 @@ No networking, no display, no audio, no driver-manager.
 password = "password"
 uid = 0
 gid = 0
-shell = "/usr/bin/zsh"
+shell = "/usr/bin/brush"
 
 [users.user]
 password = ""
-shell = "/usr/bin/zsh"
+shell = "/usr/bin/brush"
 
 [groups.sudo]
 gid = 1