estadisticas/clinico polish: drop 'borradores', standard Corregidas/No corregidas/Todas labels, Programa→Período cascade (Postgrado leaking into Período)

Elazar review of just-shipped /estadisticas/clinico (v2.45.5), 3 fixes: (a) remove the word 'borradores' — never used anywhere in the app; it came from the coder/audit proposal wording, not existing vocabulary. (b) universe toggle = standard 3 options 'Corregidas' / 'No corregidas' / 'Todas' (replaces corregidas-default + borradores; Todas = both, no privacy concern since suppression removed). (c) Programa filter shows grado/postgrado (undergraduate/graduate); Período = the specific class/cohort the user wants. BUG: the Período dropdown currently lists both '2026-1c-grado' AND 'Postgrado' — a programa is leaking in as a período option. Expected: Período options CASCADE from the selected Programa (Programa=grado → only grado cohorts like 2026-1c-grado; Programa=Postgrado → only postgrado cohorts), and no bare programa label appears in the Período list. db: investigate why 'Postgrado' surfaces as a período (periodos row naming? unscoped list?) — coder wires the Programa→Período cascade + the a/b label changes. Class-S read-layer/UI (no auth/schema/email change; gate + PII-exclusion stay).