Archive clip URLs

Every clip URL should have a durable Wayback snapshot. The repository command
checks for an existing snapshot before requesting a new authenticated capture.

When adding or changing a clip

1. Edit coltrane/content/clips.yaml.
2. Run make archive-clips.
3. Review the added archive_url or archive_exemption.
4. Run make check-clip-archives.
5. Run make check.

The capture command saves after every URL, so it is safe to rerun after a
network error. Use the Python command directly with --limit for a controlled
batch:

uv run python -m scripts.archive_clips archive --limit 10

Creating a new snapshot requires SAVEPAGENOW_ACCESS_KEY and
SAVEPAGENOW_SECRET_KEY. Never print or commit either value. Existing
snapshots can be found without credentials.

Only use archive_exemption when Wayback cannot capture the page. Keep the
reason short and specific. Do not add an exemption merely to bypass the check.