Automate UMLS data download and artifact build pipeline

[AlexMikhalev]

Summary

Script to authenticate with UMLS API, download release files, filter to relevant subsets, and rebuild automata artifacts.

Details

• Replaces manual download process
• Complements/supersedes feat: Python backup script to download SNOMED CT without UMLS API key #35 (Python SNOMED download script)
• UMLS API supports programmatic access with API key authentication
• Key files to download: MRCONSO.RRF, MRREL.RRF, MRSTY.RRF
• Filter to relevant SABs (SNOMEDCT_US, RXNORM, NCI, NDFRT, ICD11)
• Rebuild umls_automata.bin.zst artifact after download
• Should be runnable in CI for periodic updates

Acceptance Criteria

• Script authenticates with UMLS API using stored credentials
• Downloads and extracts required RRF files
• Filters to relevant vocabularies
• Rebuilds automata artifact
• Can run headless in CI environment
• Documented in README

See also: #35

Priority: P3