Load `docker-compose.override.yml` when ClawDock builds its explicit Docker Compose file list, preserving standard Compose override behavior while keeping `docker-compose.extra.yml` as the final OpenClaw overlay.
Update Docker docs so manual Compose users include the same override order, and keep the regression test for the generated `_clawdock_compose` arguments.
Fixes#49909.
Thanks @spacegeologist.
Co-authored-by: zhengzuo0-ai <zheng.zuo0@gmail.com>