Add maintained Apache/PHP container

[karlg100]

Summary

• add a maintained Apache/PHP image and Compose setup under contrib/container
• keep runtime configuration external and managed data outside the web root
• add opt-in generic feature gates needed by the container security profile
• document configuration, build, start, logs, and shutdown

Validation

• Docker Buildx checks pass
• Compose configuration passes and requires a deployment-specific project name
• image builds from pristine upstream source
• runtime smoke covers health, login, create/edit/download, persistence, feature gates, private-file denial, read-only root filesystem, TLS session cookies, and query-free logs