feature: If commands such as `agents list` return 401, tell user to try `rossoctl login`

[esnible]

Feature Description

I'm always frustrated when rossoctl agents list outputs

Error: http://rossoctl-ui.localtest.me:8080/api/v1/agents?namespace=team1 returned 401: {"detail":"Token signing key not found"}

Proposed Solution

Instead of, or in addition to, the error message, we should suggest login for 401 errors.

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Additional Context

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