Copilot review on PR #15: the 'gate off' wording in AGENTS.md and
.env.example read as 'no assignee', but read_task() always parses the
Assignee line and the card face always renders it. The gate governs only
whether a move writes/clears the line and commits. Reword both to say so.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>