- Add new `DOCKER_MODE` form field to choose between `dood` and `dind` modes, removing old `PRIVILEGED` mode field and `-dind` variant application
- Update `docker-compose.yml` to conditionally include `dind` service based on mode, and refactor `init.sh` to dynamically set `DOCKER_HOST` environment variable
- Refactor `register.sh` to handle both modes, configure runner accordingly, update default values for registration fields, and define the default job container base image as node:lts
- Update README with detailed security risk warnings for both modes, remove version selection instructions, and add usage examples for custom container images and installing docker client in workflows
