Add dual-path ISO build scripts (Arch + Debian) with README

- iso/build.sh: Debian/Ubuntu host builder using debootstrap + xorriso
  Bootstraps Debian bookworm, compiles OrionOS in chroot, produces
  bootable hybrid ISO with GRUB (BIOS + EFI), auto-login root on tty1
- iso/build-arch.sh: Arch Linux host builder using mkarchiso
  Compiles OrionOS, installs into archiso profile, runs mkarchiso
- iso/README.md: instructions for all three paths (Docker/Debian/Arch)
  including dd and Ventoy USB flashing
- Makefile: iso target auto-detects available tool (docker/debootstrap/mkarchiso)

iso/build-arch.sh

@@ -0,0 +1,37 @@
+#!/usr/bin/env bash
+# OrionOS ISO builder — Arch Linux host using mkarchiso
+# Run as root from the repo root: sudo bash iso/build-arch.sh
+set -euo pipefail
+
+REPO="$(cd "$(dirname "$0")/.." && pwd)"
+OUT="$REPO/iso/output"
+
+echo "==> Building OrionOS binaries..."
+cd "$REPO"
+make all
+
+echo "==> Installing OrionOS binaries into profile airootfs..."
+install -Dm755 wm/orionwm               iso/profile/airootfs/usr/local/bin/orionwm
+install -Dm755 deskbar/oriondeskbar     iso/profile/airootfs/usr/local/bin/oriondeskbar
+install -Dm755 launcher/orionlauncher   iso/profile/airootfs/usr/local/bin/orionlauncher
+install -Dm755 orionnotify/orionnotify  iso/profile/airootfs/usr/local/bin/orionnotify
+install -Dm755 orionlock/orionlock      iso/profile/airootfs/usr/local/bin/orionlock
+install -Dm755 orionshot/orionshot      iso/profile/airootfs/usr/local/bin/orionshot
+install -Dm755 orionclip/orionclip      iso/profile/airootfs/usr/local/bin/orionclip
+install -Dm755 orionpkg/orionpkg        iso/profile/airootfs/usr/local/bin/orionpkg
+install -Dm755 themes/orionwallpaper    iso/profile/airootfs/usr/local/bin/orionwallpaper
+mkdir -p iso/profile/airootfs/usr/share/themes
+cp -r themes/OrionOS iso/profile/airootfs/usr/share/themes/
+install -Dm644 themes/picom.conf        iso/profile/airootfs/etc/orionos/picom.conf
+mkdir -p iso/profile/airootfs/usr/share/orionos/wallpapers
+bash themes/wallpapers/generate-default.sh 2>/dev/null || true
+cp -f themes/wallpapers/orionos-default.png \
+      iso/profile/airootfs/usr/share/orionos/wallpapers/ 2>/dev/null || true
+
+echo "==> Running mkarchiso..."
+mkdir -p "$OUT"
+mkarchiso -v -w /tmp/orionos-arch-work -o "$OUT" iso/profile
+
+echo ""
+echo "✓ ISO built in $OUT"
+ls -lh "$OUT"/*.iso 2>/dev/null || true