Refactor ISO build for the package-backed install flow

The ISO no longer carries a cp -r'd copy of the omarchy git checkout
into /root/omarchy and the target /home/$user/.local/share/omarchy.
Instead it builds omarchy-installer + omarchy-settings + omarchy +
omarchy-limine from mounted source trees (${OMARCHY_INSTALLER_PATH:-
../omarchy-installer} and ${OMARCHY_PKGS_PATH:-../omarchy-pkgs}),
drops them in the offline mirror, and pacstraps omarchy-installer
during the target install — which deps-in the other three.

- builder/build-omarchy-packages.sh: new. Builds the four packages
  inside the ISO build container using each PKGBUILD's OMARCHY_SRC
  override (introduced in Chunk 2). Creates a 'builder' user because
  makepkg refuses to run as root. Drops the resulting .pkg.tar.zst
  files into the offline-mirror directory.

- builder/build-iso.sh: drop the git clone / -v omarchy mount path;
  call build-omarchy-packages.sh first; filter out the locally-built
  package names from the rest-of-mirror download so we don't try to
  fetch them from the network mirror.

- configs/airootfs/root/.automated_script.sh: replace the install_omarchy
  cp-and-source dance with 'arch-chroot pacman -S omarchy-installer'
  followed by 'OMARCHY_INSTALL_MODE=offline omarchy-install'. Drop the
  big chown/chmod block that was setting up the cloned tree.
  use_omarchy_helpers extracts the installer's helpers/ tree directly
  from the offline-mirror's omarchy-installer-*.pkg.tar.zst so the live
  ISO has access to gum-styled logging before pacstrap.

- bin/omarchy-iso-make: always mount omarchy-installer and omarchy-pkgs
  (paths configurable via OMARCHY_INSTALLER_PATH / OMARCHY_PKGS_PATH;
  default to ../omarchy-installer and ../omarchy-pkgs). --local-source
  is now a back-compat no-op.

builder/build-omarchy-packages.sh

@@ -0,0 +1,72 @@
+#!/bin/bash
+# Build omarchy + omarchy-settings + omarchy-installer + omarchy-limine from
+# mounted source (/omarchy-installer + /omarchy-pkgs) and drop the .pkg.tar.zst
+# files into the offline-mirror directory passed as $1.
+#
+# Run inside the ISO build container (build-iso.sh sources this).
+
+set -e
+
+offline_mirror_dir="$1"
+if [[ -z $offline_mirror_dir ]]; then
+  echo "Usage: build-omarchy-packages.sh <offline-mirror-dir>" >&2
+  exit 1
+fi
+
+if [[ ! -d /omarchy-installer ]]; then
+  echo "ERROR: /omarchy-installer not mounted (pass --local-source or set OMARCHY_INSTALLER_PATH)" >&2
+  exit 1
+fi
+if [[ ! -d /omarchy-pkgs ]]; then
+  echo "ERROR: /omarchy-pkgs not mounted (set OMARCHY_PKGS_PATH or place ../omarchy-pkgs)" >&2
+  exit 1
+fi
+
+work_dir=/tmp/omarchy-pkg-build
+rm -rf "$work_dir"
+mkdir -p "$work_dir"
+
+# makepkg refuses to run as root; create a builder user with passwordless
+# sudo for pacman dep installation during the build.
+if ! id builder &>/dev/null; then
+  useradd -m -s /bin/bash builder
+fi
+echo 'builder ALL=(ALL) NOPASSWD: /usr/bin/pacman' > /etc/sudoers.d/99-omarchy-pkg-builder
+chmod 440 /etc/sudoers.d/99-omarchy-pkg-builder
+
+pacman -Sy --noconfirm
+
+# Order matters: omarchy depends on omarchy-settings/-installer which depend on
+# the base packages; omarchy-installer depends on the others. Build leaves
+# first so dependents can pacman -S them from /tmp once needed. We don't
+# actually install during the build, so the order is mostly cosmetic — but
+# keeping it stable helps logs.
+packages=(
+  omarchy-limine
+  omarchy-settings
+  omarchy
+  omarchy-installer
+)
+
+for pkg in "${packages[@]}"; do
+  echo "----------------------------------------"
+  echo "Building $pkg"
+  echo "----------------------------------------"
+  pkg_work="$work_dir/$pkg"
+  cp -a "/omarchy-pkgs/pkgbuilds/$pkg" "$pkg_work"
+  chown -R builder:builder "$pkg_work"
+
+  su builder -c "
+    cd '$pkg_work' &&
+    PKGDEST='$work_dir' \
+    OMARCHY_SRC=/omarchy-installer \
+    makepkg --noconfirm --skippgpcheck --skipchecksums -s -f
+  "
+done
+
+mkdir -p "$offline_mirror_dir"
+mv "$work_dir"/*.pkg.tar.zst "$offline_mirror_dir/"
+
+echo
+echo "Built omarchy packages, placed in $offline_mirror_dir:"
+ls "$offline_mirror_dir"/omarchy*.pkg.tar.zst | sed 's|^|  |'