docker_service.get_container_info() was calling self._docker_client._get_container_info()
but AsyncDockerClient didn't have this method, causing silent AttributeError and
returning None, which triggered false health check failures.
Added _get_container_info() using aiodocker's container.show() to properly retrieve
container state information for health monitoring.
- Fix docker client initialization bug in app.py (context manager was closing client)
- Add restart_session() method to preserve session IDs during container restarts
- Add 60-second startup grace period before health checking new sessions
- Fix _stop_container and _get_container_info to use docker_service API consistently
- Disable mDNS in Dockerfile to prevent Bonjour service name conflicts
- Remove old container before restart to free port bindings
