Align Medicaid Stage 1 validator to 2025 targets

[daphnehanse11]

Fixes #971

Summary

• Refresh medicaid_enrollment_2025.csv to Medicaid.gov updated December 2025 final-report total_medicaid_enrollment values.
• Point the enhanced and sparse Stage 1 Medicaid validators at the 2025 target file for the 2025 medicaid_enrolled calculation.
• Remove the temporary Stage 1 skip marker now that the validator is aligned.

Source

• Data.Medicaid.gov dataset 6165f45b-ca93-5bb5-9d06-db29c692a360, filtered to reporting_period=202512 and preliminary_or_updated=U.
• All 51 rows report final_report=Y; target values use total_medicaid_enrollment, not combined Medicaid and CHIP enrollment.

Testing

• uv run pytest tests/unit/calibration/test_loss_targets.py -q
• uv run ruff format --check validation/stage_1/conftest.py validation/stage_1/test_enhanced_cps.py validation/stage_1/test_sparse_enhanced_cps.py tests/unit/calibration/test_loss_targets.py
• uv run ruff check validation/stage_1/conftest.py validation/stage_1/test_enhanced_cps.py validation/stage_1/test_sparse_enhanced_cps.py tests/unit/calibration/test_loss_targets.py

Note: targeted local Stage 1 Medicaid validation did not reach the assertion because the local enhanced_cps_2024.h5 fixture fails to load with a pre-existing weeks_unemployed person-count shape mismatch.