fix: error messages

[ciehanski]

dpctl deployment errors reported an all-clear for a name that doesn't exist. The reports route answers an unknown app with an empty list rather than a 404, so a typo looked exactly like a healthy deployment, and a CI job checking for failures would have read it as a pass. It now confirms the deployment exists before saying there are no failures, and only pays for that check when the result is empty.

Server errors printed as raw JSON: [Error] {"message":"This access key is read-only..."}. Three places were unwrapping the envelope and disagreeing about how; they now share one helper. Read-only keys hit this constantly, so it showed up on every refused write.

dpctl org, dpctl app and five other bare category commands printed Argument check failed: (argv) => isValidCommand under the usage block. .fail() deduped only identical messages, so the arity complaint and the check's stringifiedsource both got through.