EVO-123: convert 11 UPDATE OF invariant guards to AFTER/no-column-list

EVO-123 / evolutiva-db.md R5. Convert each final-row-invariant UPDATE OF guard: no column list, OLD.x IS DISTINCT FROM NEW.x in body, AFTER (or constraint trigger), forced-red arm where a neighbouring BEFORE trigger does the rewrite. Write-shaping triggers keep UPDATE OF. Latent today (no rewriter found), hence p2; raise if a migration adds a BEFORE trigger that assigns a watched column. Done = every guard listed converted and its forced-red arm recorded. Guards (live catalog, 11): lookupOptions endo1Tratamiento/materia/trainingActivity reference_guard; periodos endo1ClinicalShape_parent, materiaOption_valid, trainingActivity_parent; practicas endo1ClinicalShape_parent, trainingActivity_parent; practicaImages validate_practica_image_scope; studentExamScores validateLookups; users admin_invariant.