cdifCodelist: add version, maintaining-agency, and parent-scheme properties

[smrgeoinfo]

Summary

The cdifCodelist profile (skos:ConceptScheme code list) has no property for a code list's version, maintaining agency, or parent scheme. This gap surfaced while building the DDI→CDIF crosswalk in the validation repo (OHDSI project).

Where it came up

DDI Codebook 2.5 docDscr/controlledVocabUsed and DDI code-list declarations carry, per the SDMX-aligned model:

DDI field	intended CDIF target	status
codeListName	skos:prefLabel	mapped ✅
codeListID	schema:identifier	mapped ✅
codeListURN	schema:identifier (also @id)	mapped ✅
codeListVersionID	(version of the code list)	no cdifCodelist property
codeListAgencyName	(maintaining agency/organization)	no cdifCodelist property
codeListSchemeURN	(URN of the containing/parent scheme)	no cdifCodelist property

The mapped rows are in converters/mappings/ddi25-to-cdif.sssom.tsv; the three unmapped ones are flagged there as awaiting a cdifCodelist target.

Proposed additions to cdifCodelist

• version — schema:version on the ConceptScheme (string).
• maintaining agency — an organization/agency reference. Options: schema:publisher (schema.org) or a schema:subjectOf catalog-record schema:maintainer; SKOS convention would be dcterms:creator/dcterms:publisher. Pick one consistent with the profile's agent modelling.
• parent scheme — a link from a ConceptScheme to a containing scheme (the SDMX "codelist scheme"). No native SKOS property exists for scheme→scheme; candidates: schema:isPartOf, or a cdif: link.

These are additive, optional properties (no existing code list becomes invalid).

Scope note

Building-block change (Layer A), separate from the DDI conversion work that revealed it. Filing here so the converter can stay a pure consumer; if accepted, the three SSSOM rows above can then point at real targets.