Add a Rocky Linux 9 virtual machine

run-rocky9.py with its QEMU config, port forwards (SSH on 2226) and
cloud-init seed, modelled on the Fedora 44 launcher. Update vm-images for
the rocky9 download target.

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

seediso/rocky9/build-seed.sh

@@ -0,0 +1,62 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+script_dir="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)"
+output="${1:-${script_dir}/seed.iso}"
+files=(user-data meta-data)
+
+# Public key injected into user-data: $SSH_PUBKEY_FILE, else the first
+# ~/.ssh/id_*.pub, else the first key offered by ssh-agent.
+pubkey=""
+if [[ -n "${SSH_PUBKEY_FILE:-}" ]]; then
+  pubkey="$(head -n1 -- "${SSH_PUBKEY_FILE}")"
+else
+  for f in "${HOME}"/.ssh/id_ed25519.pub "${HOME}"/.ssh/id_*.pub; do
+    if [[ -f "$f" ]]; then pubkey="$(head -n1 -- "$f")"; break; fi
+  done
+  if [[ -z "$pubkey" ]] && command -v ssh-add >/dev/null 2>&1; then
+    pubkey="$(ssh-add -L 2>/dev/null | head -n1 || true)"
+  fi
+fi
+if [[ "$pubkey" != ssh-* && "$pubkey" != ecdsa-* && "$pubkey" != sk-* ]]; then
+  printf 'Error: no SSH public key found; set SSH_PUBKEY_FILE.\n' >&2
+  exit 1
+fi
+
+work="$(mktemp -d)"
+trap 'rm -rf -- "${work}"' EXIT
+template="$(<"${script_dir}/user-data")"
+printf '%s\n' "${template//@SSH_PUBKEY@/${pubkey}}" > "${work}/user-data"
+cp -- "${script_dir}/meta-data" "${work}/meta-data"
+if [[ -f "${script_dir}/network-config" ]]; then
+  cp -- "${script_dir}/network-config" "${work}/network-config"
+fi
+
+mkdir -p "$(dirname -- "$output")"
+
+if [[ -f "${script_dir}/network-config" ]]; then
+  files+=(network-config)
+fi
+
+if command -v cloud-localds >/dev/null 2>&1; then
+  args=()
+  if [[ -f "${script_dir}/network-config" ]]; then
+    args+=(--network-config="${work}/network-config")
+  fi
+  cloud-localds "${args[@]}" "${output}" \
+    "${work}/user-data" "${work}/meta-data"
+elif command -v xorriso >/dev/null 2>&1; then
+  xorriso -as mkisofs -quiet -volid cidata -joliet -rock \
+    -output "${output}" "${files[@]/#/${work}/}"
+elif command -v genisoimage >/dev/null 2>&1; then
+  genisoimage -quiet -output "${output}" -volid cidata -joliet -rock \
+    "${files[@]/#/${work}/}"
+elif command -v mkisofs >/dev/null 2>&1; then
+  mkisofs -quiet -output "${output}" -volid cidata -joliet -rock \
+    "${files[@]/#/${work}/}"
+else
+  printf 'Error: install cloud-image-utils, xorriso, genisoimage, or mkisofs.\n' >&2
+  exit 1
+fi
+
+printf 'Created %s\n' "${output}"