feat: --defaults applies the default setup without the menu, also from an installer (no session): the base for a Steam Machine ISO

systemctl --user goes through user_systemctl, which only changes unit files
without a session; the theme lets Plasma build Vapor's layout at the first
login when the layout is still /etc/skel's; a one-time first-login autostart
sets up single user's launcher and opens the app.

lib/first-login.sh

@@ -0,0 +1,40 @@
+#!/bin/bash
+# The ISO applies Steamify in the installer, before the user ever logged
+# in (steamify.sh --defaults without a session). What needs Plasma's first
+# layout is finished at the first desktop login, by a one-time autostart
+# that then opens the app, next to CachyOS Hello.
+# Sourced by steamify.sh; not meant to be run on its own.
+
+FIRST_LOGIN_ENTRY="${XDG_CONFIG_HOME:-$HOME/.config}/autostart/steamify-first-login.desktop"
+FIRST_LOGIN_SCRIPT="$STEAMIFY_BIN/first-login"
+
+first_login_schedule() {
+    install_executable "$FIRST_LOGIN_SCRIPT" 755 << EOF2
+#!/bin/bash
+# Installed by Steamify CachyOS: runs once, at the first desktop login.
+set -o pipefail
+curl -fsSL --max-time 30 "$WIZARD_URL" | bash -s -- --first-login
+rm -f "$FIRST_LOGIN_ENTRY" "\$0"
+[[ -x "$WIZARD_APP_LAUNCHER" ]] && exec "$WIZARD_APP_LAUNCHER"
+EOF2
+    printf '%s\n' '[Desktop Entry]' 'Type=Application' 'Name=Steamify first login' \
+        "Exec=$FIRST_LOGIN_SCRIPT" 'OnlyShowIn=KDE;' 'X-KDE-autostart-phase=2' 'NoDisplay=true' |
+        install_executable "$FIRST_LOGIN_ENTRY" 644
+}
+
+first_login_run() {
+    # plasmashell has just laid out the desktop from the look-and-feel
+    # package; wait for its config, then put single user's launcher
+    # settings on the new launcher.
+    local _
+    for _ in $(seq 30); do
+        [[ -n "$(plasma_applets org.kde.plasma.kickoff)" ]] && break
+        sleep 2
+    done
+    if single_status; then
+        stop_plasmashell_for_edit
+        single_launcher
+        restart_plasmashell_if_stopped
+    fi
+    return 0
+}