MARS-526 fast-follow: focused action tests for updateAlumno hardening — null-JTP orphan (vs MARS-29), stale-updatedAt lost-update rejection, closed-periodo/period-scope guard. Audit noted as coverage gap, non-blocking.

audit-mars-ca flagged missing focused tests on the updateAlumno guards shipped in c1e8657 (v2.47.1): assert (a) null-JTP orphan is rejected per MARS-29, (b) a stale optimistic-updatedAt write is rejected, (c) comisión-active/period-scope check rejects out-of-scope. Non-blocking fast-follow.