feat: Steamify's choices in the installer: a Steam Machine page (what to leave out) and a Start in page (gaming mode or desktop), passed to steamify.sh --defaults

archiso/airootfs/etc/calamares/modules/packagechooser_steamifyboot.conf

@@ -0,0 +1,16 @@
+# Steamify: where the Steam Machine starts (steamify-install passes --boot).
+---
+mode: required
+method: legacy
+labels:
+    step: "Start in"
+default: gamescope
+items:
+    - id: gamescope
+      name: "Gaming mode"
+      description: "Start straight into Steam's gaming mode, like SteamOS. Switch to Desktop in Steam's power menu brings you to the desktop."
+      screenshot: ":/images/no-selection.png"
+    - id: desktop
+      name: "Desktop"
+      description: "Start in the Plasma desktop. Return to Gaming Mode on the desktop brings you to Steam's gaming mode."
+      screenshot: ":/images/no-selection.png"

archiso/airootfs/etc/calamares/modules/packagechooser_steamifyskip.conf

@@ -0,0 +1,37 @@
+# Steamify: which parts of the Steam Machine setup to leave out. Nothing
+# selected means Steamify's full default setup; the ids are Steamify's menu
+# items (steamify-install passes them as --skip).
+---
+mode: optionalmultiple
+method: legacy
+labels:
+    step: "Steam Machine"
+items:
+    - id: ""
+      name: "Everything"
+      description: "Select what to leave out of the Steam Machine setup (Steamify). Leave everything unselected for the full SteamOS-style setup; everything can be changed later in the Steamify app."
+      screenshot: ":/images/no-selection.png"
+    - id: theme
+      name: "Leave out: SteamOS theme"
+      description: "The Vapor look for the desktop, with SteamOS's panel layout and Add to Steam."
+    - id: glyphs
+      name: "Leave out: Steam Deck/Machine icons"
+      description: "Steam Deck button icons in gaming mode."
+    - id: single
+      name: "Leave out: single user mode"
+      description: "No password, lock screen, user switching or log out, like SteamOS."
+    - id: launcher
+      name: "Leave out: Steamify shortcut"
+      description: "The Steamify app on the desktop and in the launcher, to change these choices later."
+    - id: notify
+      name: "Leave out: update notifications"
+      description: "A notification when there's a new Steamify. It never updates by itself."
+    - id: vram
+      name: "Leave out: VRAM booster"
+      description: "The game in front keeps its video memory; background apps make room."
+    - id: cec
+      name: "Leave out: HDMI-CEC"
+      description: "Use Steam with the TV remote, TV on and off with the Steam Machine."
+    - id: machine
+      name: "Leave out: Steam Machine support"
+      description: "The LED bar driver, hardware settings in Steam and the power-off fix."

archiso/airootfs/etc/calamares/modules/shellprocess_steamify.conf

@@ -4,7 +4,7 @@
 dontChroot: true
 timeout: 3600
 script:
-    - "-/usr/local/bin/steamify-install ${ROOT} ${USER}"
+    - "-/usr/local/bin/steamify-install ${ROOT} ${USER} \"${gs[packagechooser_steamifyskip]}\" \"${gs[packagechooser_steamifyboot]}\""
 
 i18n:
     name: "Setting up the Steam Machine (Steamify)"