feat(nodes): add headless one-liner provisioning ...

- New /api/v1/nodes/provision/{node_id} endpoint returns a python install script.\n- New /api/v1/agent/installer endpoint serves the bootstrap_installer.py script.\n- UI updated with code snippet and copy-to-clipboard for rapid headless deployment.

refactor: re-org frontend folder structure to simply be 'frontend' ...

- Moved ui/client-app to frontend/

- Updated README and documentation references

- Updated docker-compose, local run scripts, and remote deploy scripts to point to new frontend location