Agree on Unicode versus ASCII in comments and documentation

Recent Eidos-related PRs include many unrelated changes that replace Unicode symbols with ASCII equivalents. These changes add noise to the diff and make the substantive changes harder to review.

We should agree on a repository-wide convention: allow Unicode symbols in comments and documentation, or standardize on ASCII. If Unicode remains allowed, we should clarify any restrictions.

Once we decide, a dedicated PR should:

- Apply the convention consistently across the repository in one batch.
- Update repository guidance, including `AGENTS.md` and relevant documentation, so contributors and agents follow it.
- Keep this cleanup separate from functional changes.

Until then, we should avoid incidental Unicode-to-ASCII replacements in unrelated PRs.