RFC: MLflow Integration for Healthcare Experiment Tracking

Proposes healthcare-specific context helpers and FHIR Provenance
generation for MLflow experiment tracking. Complements (not wraps)
MLflow with HealthcareRunContext, PatientContext, and
log_healthcare_context() helper function.

Related to #185

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: adamkells