3 new tables + idempotent DDL migration (prod guard: refuses DB name cma without approval): tax_filing_log (P_TAX_TIMELY), hr_monthly_ledger (L_EMPLOYEE_TURNOVER), licence_ledger (P_LICENCE_OK).
Entry API /api/cma/ext-ledger: create / CSV batch import / query by entity+period / derive trigger. on_time is server-derived only; HR rows rejected when end != begin + hires - separations.
Deriver writes kpi_values only (source_type=derived, idempotent upsert); denominator 0 returns None and writes nothing; never creates or changes kpi_definitions.
Tests: 22 new pytest cases (22 passed); scratch-DB e2e battery 28 assertions PASS with zero production write.
