Support arm64 hosts in the Windows 11 launcher

Pick qemu-system-aarch64, the AArch64 UEFI firmware and a per-architecture
QEMU config (NVMe disk, virtio-net, ramfb, USB installation media) on arm64,
render the answer file for the target architecture, and move the q35-only
disk and NIC devices out of the shared config. Update vm-images to match
arm64 Windows ISO names.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

seediso/windows11/build-seed.sh

@@ -3,8 +3,22 @@ set -euo pipefail
 
 script_dir="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)"
 output="${1:-${script_dir}/seed.iso}"
+arch="${2:-${VM_IMAGE_ARCH:-$(uname -m)}}"
+case "$arch" in
+  arm64|aarch64) answer_arch=arm64 ;;
+  x86_64|amd64) answer_arch=amd64 ;;
+  *) printf 'Error: unsupported architecture: %s\n' "$arch" >&2; exit 1 ;;
+esac
+
+# The answer file's components name the processor architecture, so render a
+# copy for the target architecture.
+work_dir="$(mktemp -d)"
+trap 'rm -rf "$work_dir"' EXIT
+sed "s/processorArchitecture=\"amd64\"/processorArchitecture=\"${answer_arch}\"/" \
+  "$script_dir/Autounattend.xml" >"$work_dir/Autounattend.xml"
+
 seed_files=(
-  "$script_dir/Autounattend.xml"
+  "$work_dir/Autounattend.xml"
   "$script_dir/Configure-Windows.ps1"
 )
 # Numbered installer scripts (10-Install-Git.bat, 20-..., in install order).