Make setup ISO-only

Remove legacy online installer entrypoints, collapse migrations for 4.0, and move setup responsibilities into target-side system, hardware, and user commands.

install/user/hardware/asus/fix-audio-mixer.sh

@@ -0,0 +1,13 @@
+# Fix audio volume on Asus ROG laptops by using a soft mixer.
+
+if omarchy-hw-asus-rog; then
+  mkdir -p ~/.config/wireplumber/wireplumber.conf.d/
+  cp "$OMARCHY_PATH/default/wireplumber/wireplumber.conf.d/alsa-soft-mixer.conf" ~/.config/wireplumber/wireplumber.conf.d/
+  rm -rf ~/.local/state/wireplumber/default-routes
+
+  # Unmute the Master control on the ALC285 card (often muted by default)
+  card=$(aplay -l 2>/dev/null | grep -i "ALC285" | head -1 | sed 's/card \([0-9]*\).*/\1/')
+  if [[ -n $card ]]; then
+    amixer -c "$card" set Master 80% unmute 2>/dev/null
+  fi
+fi