Integrate UMLS MRREL relationships into knowledge graph

[AlexMikhalev]

Summary

Import MRREL (relationship) table from UMLS into MedicalRoleGraph to add clinically-backed relationships.

Details

• Currently have 65 edge types in MedicalRoleGraph
• MRREL provides drug-drug interactions, gene-disease associations, procedure-indication links
• Key relationship types: may_treat, has_ingredient, gene_associated_with_disease, contraindicated_with
• Filter MRREL to relevant SABs (SNOMEDCT_US, RXNORM, NCI, NDFRT) to keep graph manageable
• Each imported relationship gets a source attribution for auditability

Acceptance Criteria

• Parse MRREL.RRF and filter to relevant relationship types
• Import into MedicalRoleGraph with proper edge typing
• Document new edge types added
• Knowledge graph queries return richer evidence paths
• No regression in existing 18 eval cases

Priority: P2