argparse requires exactly one action, so the documented diagnostic form
`--print-effective-config --config … --start` never took the early-return
branch in main.run(): it printed the resolved config and then executed a
real do_start(), silently replacing a running container with the [default]
model. README, installation guide and manual all recommended that form.
Make it an action in the mutually exclusive group. It can no longer be
combined with --start/--check/--stop/--change/--chat (argparse error,
exit 2), and it skips the docker_available() check, so it now really is
the offline config check the docs promise. --dry-run remains a modifier
and still requires a reachable daemon.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>