Add rocky9-system image using distribution libraries

Install libraries from Rocky Linux 9, CRB and EPEL instead of building
from source; packages missing from those repositories are skipped.

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

rocky9-system/build.sh

@@ -0,0 +1,19 @@
+#!/bin/sh
+
+set -eu
+
+IMAGE_NAME="${IMAGE_NAME:-rocky9-system-stack}"
+SCRIPT_DIR=$(CDPATH= cd -- "$(dirname -- "$0")" && pwd)
+
+if command -v podman >/dev/null 2>&1; then
+    ENGINE=podman
+elif command -v docker >/dev/null 2>&1; then
+    ENGINE=docker
+else
+    echo "Error: Podman or Docker is required." >&2
+    exit 1
+fi
+ENGINE="${CONTAINER_ENGINE:-$ENGINE}"
+
+echo "Building image $IMAGE_NAME with $ENGINE ..."
+exec "$ENGINE" build --tag "$IMAGE_NAME" "$SCRIPT_DIR"