Add ISO user config: unattended install needs baked accounts

VM smoke test of the first ISO reached GDM but no user existed
(bootc-image-builder ISOs install unattended; gnome-initial-setup is
not in the bazzite base). iso-config.toml creates parent (wheel) and
kid with placeholder passwords to change on first login.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

iso-config.toml

@@ -0,0 +1,15 @@
+# bootc-image-builder customizations for the installer ISO.
+# Mount as /config.toml on the bib container (see BUILD-CONSOLE.md).
+#
+# PLACEHOLDER PASSWORDS — change both on first login:
+#   passwd            (for the account you're logged into)
+#   sudo passwd kid   (parent can reset the kid's password)
+
+[[customizations.user]]
+name = "parent"
+password = "bc250console"
+groups = ["wheel"]
+
+[[customizations.user]]
+name = "kid"
+password = "bc250console"