Add ARM64 ISO build for Apple Silicon / UTM

- iso/docker/Dockerfile.arm64: Arch Linux ARM base (menci/archlinuxarm:aarch64)
- iso/docker/entrypoint-arm64.sh: ARM64 archiso profile — linux-aarch64
  kernel, EFI-only boot (no syslinux), aarch64 squashfs path, spice-vdagent
  for UTM clipboard, VirtIO GPU modesetting config
- build-iso-arm64.sh: docker buildx --platform linux/arm64 wrapper;
  runs natively on Apple Silicon, no QEMU emulation needed

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

build-iso-arm64.sh

@@ -0,0 +1,101 @@
+#!/usr/bin/env bash
+# OrionOS ARM64 ISO builder — for Apple Silicon Macs (runs natively, no emulation).
+# On Intel Macs, this uses QEMU arm64 emulation (much slower).
+#
+# Requirements: Docker Desktop with "Use Rosetta for x86_64/amd64 emulation" OFF
+#               (Rosetta emulation is for x86, not needed here)
+#
+# Usage:  ./build-iso-arm64.sh
+# Output: dist/orionos-arm64-<date>.iso
+set -euo pipefail
+
+REPO="$(cd "$(dirname "$0")" && pwd)"
+DIST="$REPO/dist"
+IMAGE="orionos-builder-arm64"
+ISO_TAG="orionos-arm64-$(date +%Y%m%d)"
+
+# ── preflight ─────────────────────────────────────────────────────────
+if ! command -v docker &>/dev/null; then
+    echo ""
+    echo "  Docker is not installed."
+    echo "  Install Docker Desktop: https://www.docker.com/products/docker-desktop/"
+    exit 1
+fi
+
+if ! docker info &>/dev/null; then
+    echo ""
+    echo "  Docker is not running. Open Docker Desktop and re-run."
+    exit 1
+fi
+
+# Ensure buildx is available (ships with Docker Desktop)
+if ! docker buildx version &>/dev/null; then
+    echo ""
+    echo "  docker buildx not found. Update Docker Desktop to a recent version."
+    exit 1
+fi
+
+echo ""
+echo "┌─────────────────────────────────────────────┐"
+echo "│       OrionOS ARM64 ISO Builder              │"
+echo "│  Native on Apple Silicon — no emulation     │"
+echo "└─────────────────────────────────────────────┘"
+echo ""
+
+# ── build the builder image ───────────────────────────────────────────
+echo "Step 1/3: Building Docker image (ARM64, Arch Linux ARM base)"
+echo "          First run downloads ~400MB — cached afterwards."
+echo ""
+docker buildx build \
+    --platform linux/arm64 \
+    --load \
+    -t "$IMAGE" \
+    -f "$REPO/iso/docker/Dockerfile.arm64" \
+    "$REPO"
+
+# ── run the ISO build inside the container ────────────────────────────
+echo ""
+echo "Step 2/3: Building ISO inside ARM64 Arch Linux container..."
+echo "          (5-15 min depending on internet speed)"
+echo ""
+mkdir -p "$DIST"
+docker run \
+    --rm \
+    --privileged \
+    --platform linux/arm64 \
+    --security-opt seccomp=unconfined \
+    -v "$DIST:/dist" \
+    -e DIST=/dist \
+    "$IMAGE"
+
+# ── rename with date tag ──────────────────────────────────────────────
+echo ""
+echo "Step 3/3: Finalizing..."
+ISO="$(find "$DIST" -name "orionos-arm64*.iso" | head -1)"
+if [[ -z "$ISO" ]]; then
+    echo "ERROR: ISO not found in $DIST — check the build output above."
+    exit 1
+fi
+
+FINAL="$DIST/$ISO_TAG.iso"
+mv "$ISO" "$FINAL"
+SIZE="$(du -sh "$FINAL" | cut -f1)"
+
+echo ""
+echo "┌─────────────────────────────────────────────────────┐"
+echo "│  Done!                                               │"
+echo "│                                                      │"
+echo "│  ISO: dist/$ISO_TAG.iso"
+echo "│  Size: $SIZE"
+echo "│                                                      │"
+echo "│  Load in UTM:                                        │"
+echo "│    1. Open UTM → New VM → Virtualize                │"
+echo "│    2. Choose Linux → enable Apple Virtualization     │"
+echo "│    3. Boot ISO: select the file above               │"
+echo "│    4. Display: VirtIO GPU (recommended)             │"
+echo "│    5. Boot — OrionOS will auto-login as 'orion'     │"
+echo "│                                                      │"
+echo "│  Copy-paste between macOS and VM:                    │"
+echo "│    spice-vdagent is pre-installed and auto-started  │"
+echo "└─────────────────────────────────────────────────────┘"
+echo ""