Gate critical US Populace target fit

[MaxGhenis]

Summary

• add US release-contract gates for SOI federal income tax liability amount, SOI income tax liability returns, and SSA Social Security benefits
• fail fiscal refresh builds when present critical targets exceed the same fit tolerances
• add regression coverage using the broken release income-tax fit values so a 0.735T final estimate cannot certify against the 2.105T SOI target

Why

The broken 2026-06-17 Populace release passed the previous finite/improving loss gate despite missing core national fiscal targets: federal income tax liability amount, income-tax-liability returns, and Social Security benefits. The release contract now treats those as hard certification requirements for US releases.

Validation

• PYTHONPATH=packages/populace-data/src uv run --python 3.13 --with pytest python -m pytest packages/populace-data/tests/test_contract.py -q
• PYTHONPATH=packages/populace-build/src:packages/populace-calibrate/src:packages/populace-frame/src:packages/populace-fit/src:packages/populace-data/src uv run --python 3.13 --with pytest --with numpy --with pandas --with packaging --with h5py --with torch --with scipy python -m pytest packages/populace-build/tests/test_us_fiscal_refresh_builder.py -q
• uv run --python 3.13 ruff check packages/populace-data/src/populace/data/contract.py packages/populace-data/tests/test_contract.py tools/build_us_fiscal_refresh_release.py packages/populace-build/tests/test_us_fiscal_refresh_builder.py
• git diff --check