Returns DuckDB DDL for one scalar ClinVar fact table plus compatibility
views and append-only, source-versioned PubMed relations. Every ClinVar XML
entity is one clinvar row identified by record_kind; repeated conditions,
observations, citations, names, and text are additional rows rather than
nested values or Cartesian products. PubMed current and as-of relations use
typed source order without deleting historical facts; read-only
pubmed_literature_* views project all source versions for direct semantic
consumers. Literature sections normalize article titles to section = "title"
and abstracts to section = "abstract", retaining structured labels in
subsection. The release catalogue and small policy configuration tables
remain separate.