Fix ACA fiscal release target support

[MaxGhenis]

Summary

• Restrict the ACA marketplace source-runtime recipient domain to tax units with positive potential aca_ptc, so CMS APTC recipient targets do not select zero-PTC units and stale pre-refresh take-up flags cannot hide eligible units.
• Feed potential aca_ptc into the source-runtime assigned_aca_ptc column used for selected-plan ratio calculation, because the runtime recalibrates take-up before using that column.
• Add reviewed support exclusions for Ledger facts that the current 2024 base frame and PolicyEngine-US formulas cannot materialize with positive support: 22 state TANF cash-assistance rows, 6 SOI under-$1/income-tax or medical-deduction rows, and the AK under-$1 return count row.
• Keep the target values in Ledger only; the package records support-exclusion reasons, not hard-coded target values.

Validation

• env -u UV_FROZEN uv run --package populace-build --extra us python -m pytest packages/populace-build/tests/test_us_fiscal_targets.py packages/populace-build/tests/test_us_fiscal_refresh_builder.py::test_aca_source_runtime_refreshes_degenerate_release_inputs packages/populace-build/tests/test_us_fiscal_refresh_builder.py::test_aca_source_runtime_rejects_enrollment_only_fallback packages/populace-build/tests/test_us_source_runtime.py -q
• env -u UV_FROZEN uv run --all-packages ruff format --check tools/build_us_fiscal_refresh_release.py packages/populace-build/src/populace/build/us/fiscal_targets.py packages/populace-build/tests/test_us_fiscal_refresh_builder.py packages/populace-build/tests/test_us_fiscal_targets.py
• env -u UV_FROZEN uv run --all-packages ruff check .
• env -u UV_FROZEN uv run --all-packages python -m pytest -q
• Release-builder matrix diagnostic with JCT Ledger bundle at runtime-code commit 5dbc387 (current head 53468f4 only strengthens tests): 5,098 active targets, 0 skipped, 0 positive zero-support targets. Diagnostic artifact: /Users/maxghenis/.codex-artifacts/populace-zero-support-diagnostic-aca-domain-exclusions-r2-20260617.json.
• Local diagnostic release-builder output: /Users/maxghenis/.codex-artifacts/populace-release-builder-aca-support-pr86-20260617-r2 (local diagnostic only; skipped demographics and out-of-sample reform validation).

Related

• Addresses the release-builder side of Implement ACA marketplace take-up input materialization #74 and Materialize Marketplace selected-plan benchmark ratios and metal-level diagnostics #75.
• Leaves Migrate ACA health-input gates after PE-US take-up contract changes #76 open because the PE-US simulated_aca_take_up_if_eligible contract is not released yet.