Function resolveArticleType

Resolve the article-type slug from a manifest, tolerating historic schemas.

Resolution order (highest precedence first):

1. articleType — canonical singular field
2. articleTypeSlug — gh-aw workflow slug field
3. articleTypes[0] — pre-aggregator-pipeline plural array
4. runType — historic field on older breaking-run manifests

Each candidate is passed through stripRunSuffix so trailing -run<N> taxonomy noise never leaks into JSON-LD articleSection, the filesystem slug, or the SEO dump's article-type histogram. Falls back to 'unknown' when none of the above is a non-empty string.