The `cleveragents server serve` CLI subcommand already exists in
server.py and Dockerfile.server already uses `python -m cleveragents`
as its ENTRYPOINT with `server serve` as the CMD.
Add BDD scenarios to k8s_helm_chart.feature that explicitly verify:
- Dockerfile.server ENTRYPOINT uses `python -m cleveragents`
- Dockerfile.server CMD includes the `server serve` subcommand tokens
Add corresponding step definitions to k8s_helm_chart_steps.py.
Closes#1088