Add BayContainerManager to manage Bay container lifecycle via Docker
Engine API, similar to how BoxliteBooter manages Ship containers.
When ShipyardNeoBooter endpoint is empty or set to '__auto__', Bay is
automatically pulled, started, health-checked, and credentials are
read from the container.
- New bay_manager.py: ensure_running, wait_healthy, read_credentials
- Integrate auto-start into ShipyardNeoBooter boot/shutdown
- Reuse Bay container across sessions (unless-stopped policy)
- Friendly error messages for Docker and credential failures
zenfun
92a8e40cde