Vignettes for Cross-source variant harmonization

• Harmonizing ClinVar by VRS identity — Republishing all of ClinVar in the GKM so every variant carries a VRS identity and every classification is a structured VA-Spec statement, letting you join ClinVar to any VRS-aware dataset by identity.
• Identifying unique variants across sources with VRS — Using VRS digests to deduplicate BRCA variants pulled from ClinVar, gnomAD, LOVD, and the literature.