Install omarchy-installer + omarchy-settings into the live ISO

Two motivations:

1. Plymouth: the omarchy plymouth theme + /etc/plymouth/plymouthd.conf
   ship from omarchy-settings (theme at /usr/share/plymouth/themes/omarchy,
   plymouthd.conf via the package's post_install etc-overrides hook).
   Without omarchy-settings on the live ISO, mkarchiso builds the initrd
   with plymouth pointing at the default theme instead of Omarchy's. Now
   it picks up the Omarchy theme on boot like the installed system does.

2. Drops the .pkg.tar.zst extraction hack in .automated_script.sh:
   OMARCHY_PATH=/usr/share/omarchy is the real package install path, so
   use_omarchy_helpers no longer needs to bsdtar pieces out of the
   offline mirror into /tmp/omarchy-iso.

builder/build-iso.sh

@@ -60,7 +60,14 @@ mkdir -p "$build_cache_dir/airootfs/opt/packages/"
 cp "/tmp/$NODE_FILENAME" "$build_cache_dir/airootfs/opt/packages/"
 
 # Packages installed into the live ISO environment itself (NOT the target system).
-arch_packages=(linux-t2 git gum jq openssl plymouth tzupdate omarchy-keyring lvm2 cryptsetup parted)
+# omarchy-installer + omarchy-settings need to be HERE so:
+#   1. /usr/share/omarchy/{install,default,bin} is available to the configurator
+#      and .automated_script.sh natively (no .pkg.tar.zst extraction hack)
+#   2. omarchy-settings's post_install hook drops omarchy's plymouthd.conf into
+#      /etc/plymouth so mkinitcpio's plymouth hook picks up the Omarchy theme
+#      when mkarchiso builds the live initramfs (otherwise plymouth shows
+#      the default theme on boot).
+arch_packages=(linux-t2 git gum jq openssl plymouth tzupdate omarchy-keyring omarchy-settings omarchy-installer lvm2 cryptsetup parted)
 printf '%s\n' "${arch_packages[@]}" >> "$build_cache_dir/packages.x86_64"
 
 # Build the offline mirror: everything pacstrap might want during the target