Add centralized image version variables in group_vars/all/vars.yml for vulnerability tracking and controlled upgrades of third-party Docker images (casdoor, flower, grafana-mcp, gitea-mcp, neo4j, memcached, nginx, oauth2-proxy, rabbitmq, searxng). Update vault.yml accordingly.
Replaces the minimal project description with a comprehensive README including a component overview table, quick start instructions, common Ansible operations, and links to detailed documentation. Aligns with Red Panda Approval™ standards.
