scripts/agent_token.py mints the 'agents' guest user + token non-interactively,
writes data/agent.env (0600, gitignored, never printed). Fixes _register_outputs
dropping user_id — guest job outputs were registered ownerless, so guests could
never see or download their own results.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
