Fix ISO build pipeline for Docker on macOS

- Disable pacman alpm sandbox in Dockerfile (seccomp blocks it in BuildKit)
- Move mkarchiso from RUN to CMD so it runs with --privileged at docker run time
- Fix output path: mkarchiso now writes to /dist (matches volume mount)
- Add syslinux + imlib2 to Docker build packages and live ISO package list
- Copy syslinux/ and efiboot/ boot configs from archiso releng into profile
- Switch deprecated UEFI grub bootmodes to uefi-x64.systemd-boot
- Fix wrong package names: libpam→pam, light→brightnessctl, remove pkexec
- Set SigLevel=Never and hardcode reliable mirrors in profile pacman.conf
- Add mkinitcpio.conf with archiso hook so initrd can mount the live squashfs

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

build-iso.sh

@@ -66,7 +66,7 @@ docker run \
 # ── rename with date tag ──────────────────────────────────────────────
 echo ""
 echo "Step 3/3: Finalizing..."
-ISO="$(find "$DIST" -name "orionos*.iso" | head -1)"
+ISO="$(find "$DIST" -iname "*.iso" | head -1)"
 if [[ -z "$ISO" ]]; then
     echo "ERROR: ISO not found in $DIST — check the build output above."
     exit 1