Fix menu/launcher to use installed apps; add pcmanfm, mousepad, arandr

Menu and launcher fallback pointed to alacritty/firefox/rigel/quill
which are not in the live ISO. Switch to xterm (already installed),
pcmanfm and mousepad (now added to packages). Also add arandr for
display settings.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

iso/profile/packages.x86_64

@@ -36,6 +36,9 @@ feh
 picom
 xterm
 libnotify
+pcmanfm
+mousepad
+arandr
 
 # Audio
 alsa-utils