Formalize numeroHistoriaClinica as validated patient DNI (governance-gated)

Mars practicas.numeroHistoriaClinica is de-facto patient DNI (coder-mars-cc live read: 2226 live values, 84.2% clean 7-8-digit Argentine-DNI shape, ~97% bare numeric) but stored as unvalidated free-text HC-number with no separate documentoNumber column - DNI-by-convention, not enforced. No live PII leak: MARS-524 already excludes numeroHistoriaClinica from the clinico aggregate fact views. GOVERNANCE-GATED (patient-PII): remediation is Elazar decision, NOT a proactive mars edit. Options to present: (a) add dedicated validated documentoType/documentoNumber columns + backfill from HC where DNI-shaped + keep HC as its own field; (b) validate/normalize in place; (c) leave as-is. Feeds EVO-80 patient-DNI unification / enamel soft-SSOT. Pluto uses the same numeroHistoriaClinica free-text field - likely parallel, pending its own data check.