Function selectReaderGuideArtifacts

Filter a set of consumed artifact filenames down to the artifacts that the aggregator actually emits as top-level ## <title> sections in the rendered article — the exact set the Reader Intelligence Guide can hyperlink to.

Mirrors the same selection / de-duplication rules used by ./aggregate.ts (the article aggregator):

1. Only *.md artifacts are eligible (*.json artifacts are referenced by the audit-appendix row, not by their own section).
2. documents/*-analysis.md entries are folded into the single "Per-document intelligence" row by the caller, so they're excluded here.
3. README.md, article.md, article.<lang>.md are aggregator outputs / metadata, not analytical sections — excluded.
4. Filename-variant alias groups are de-duplicated: when more than one alias is present (e.g. election-2026-analysis.md vs election-cycle-analysis.md), only the first member encountered in AGGREGATION_ORDER is kept — matching the aggregator's "first one wins" behaviour so the link's target heading exists.

Returns artifacts ordered the same way the article body orders them: AGGREGATION_ORDER precedence first, then any remaining *.md artifacts alphabetically.