Fix ARM64 ISO build: pacman.conf repos, kernel preset, mkinitcpio

Three fixes for the 'vmlinuz-* not found' failure:

1. Override releng profile's pacman.conf to add [alarm] and [aur] repos.
   linux-aarch64 lives in [alarm] — without this the kernel package was
   silently missing from the airootfs and /boot was empty.

2. Remove linux.preset from releng airootfs (references vmlinuz-linux,
   the x86_64 kernel name that doesn't exist on ALARM).

3. Add linux-aarch64.preset to the airootfs with an 'archiso' preset entry
   (ALL_kver=/boot/vmlinuz-linux-aarch64, archiso_image=initramfs-linux-aarch64.img).
   mkarchiso looks for this 'archiso' preset to build the live initramfs.

4. Switch customize_airootfs.sh from mkinitcpio -P to mkinitcpio -p linux-aarch64
   so only the aarch64 preset runs (not the stale x86_64 linux preset).

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

iso/docker/entrypoint-arm64.sh

@@ -16,6 +16,32 @@ echo "════════════════════════
 echo ">>> Copying archiso releng profile..."
 cp -r /usr/share/archiso/configs/releng "$PROFILE"
 
+# Override the releng pacman.conf: it only has Arch Linux x86_64 repos.
+# ALARM's linux-aarch64 kernel lives in [alarm] — without this the kernel
+# package silently fails to install and /boot/vmlinuz-* is never created.
+cat > "$PROFILE/pacman.conf" <<'PACMANCONF'
+[options]
+HoldPkg     = pacman glibc
+Architecture = aarch64
+
+[core]
+Include = /etc/pacman.d/mirrorlist
+
+[extra]
+Include = /etc/pacman.d/mirrorlist
+
+[alarm]
+Include = /etc/pacman.d/mirrorlist
+
+[aur]
+Include = /etc/pacman.d/mirrorlist
+PACMANCONF
+
+# The releng profile ships linux.preset in its airootfs for x86_64 linux kernel.
+# It references /boot/vmlinuz-linux which doesn't exist on ALARM; remove it so
+# mkinitcpio doesn't try to process it and fail.
+rm -f "$PROFILE/airootfs/etc/mkinitcpio.d/linux.preset"
+
 # ── 2. Package list — ARM64 (no syslinux, no Intel GPU, no broadcom-wl)
 cat > "$PROFILE/packages.aarch64" <<'PKGS'
 base
@@ -187,6 +213,20 @@ FILES=()
 HOOKS=(base udev plymouth archiso block filesystems keyboard)
 MKCONF
 
+# mkinitcpio preset for the aarch64 live boot image.
+# mkarchiso looks for a preset named 'archiso' to build the live initramfs.
+# The linux-aarch64 package only ships 'default'/'fallback' presets, so we
+# provide our own with the archiso hooks and the correct kernel path.
+mkdir -p "$AIROOTFS/etc/mkinitcpio.d"
+cat > "$AIROOTFS/etc/mkinitcpio.d/linux-aarch64.preset" <<'PRESET'
+ALL_config="/etc/mkinitcpio.conf.d/archiso.conf"
+ALL_kver="/boot/vmlinuz-linux-aarch64"
+
+PRESETS=('archiso')
+
+archiso_image="/boot/initramfs-linux-aarch64.img"
+PRESET
+
 cat > "$AIROOTFS/etc/hostname" <<'EOF'
 orionos
 EOF
@@ -630,7 +670,9 @@ update-desktop-database 2>/dev/null || true
 fc-cache -f 2>/dev/null || true
 
 plymouth-set-default-theme orionos 2>/dev/null || true
-mkinitcpio -P 2>&1 | tail -5 || true
+# Run only the aarch64 preset — mkinitcpio -P would also try linux.preset
+# (which references the x86_64 vmlinuz-linux) and fail.
+mkinitcpio -p linux-aarch64 2>&1 | tail -10 || true
 
 mkdir -p /etc/skel
 cat > /etc/skel/.xscreensaver <<'SS'