#2726 issue --extension: documented example @adam/cfgmgmt is unroutable (no repo), so -x against it no-ops at exit 0

The -x/--extension help for issue bug/feature/security gives @adam/cfgmgmt as the example, and the references/issue docs use it too.

@adam/cfgmgmt is a real published extension whose registry repository is null (repository, repositoryVerified, repositoryVerifiedUrl all null via swamp extension search cfgmgmt). Per the current routing rules, a third-party extension with no declared repo is refused cleanly -- and refusals exit 0. So copying the documented example verbatim files nothing, with no error, indistinguishable from success.

Fixes:

1. Use an example that actually routes -- @swamp/aws (-> Lab), or a third-party extension with a verified repo (e.g. @shrug/serial-port).
2. Make a refused outcome distinguishable from a successful file -- non-zero exit, or a clear stderr/banner in text mode, not just status:"refused" at exit 0.