When maybeReexecUnderSg() re-launches setup:auto under `sg docker`,
the new process had no memory of completed steps — it re-prompted the
welcome menu, re-ran environment and container checks, and then failed
on onecli because the earlier run's state was lost.
Pass NANOCLAW_SKIP with completedStepNames() so the re-exec'd process
skips already-finished steps, suppress the welcome menu and existing-env
prompts on re-exec since the user already answered them.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>