Add CTC calibration follow-up targets and validation

[MaxGhenis]

Summary

• load national AGI-split refundable and nonrefundable CTC targets from the IRS geography file and include them in the training target config
• expand national CTC diagnostics to AGI-by-filing-status, qualifying-child-count, and qualifying-child-age tables
• add canonical ARPA-style CTC/EITC reform diagnostics to validate_national_h5 and cover the new paths with unit tests

Issue linkage

• Closes Target CTC qualifying-child composition by age and child-count buckets #718
• Closes Add canonical CTC reform diagnostics to ECPS release validation #719
• Addresses Add AGI-by-filing-status CTC targets for refundable and nonrefundable components #717

Notes

This lands the admin-backed part of #717: national AGI-band CTC targets plus AGI-by-filing-status diagnostics. I am not claiming true admin-backed filing-status-split refundable/nonrefundable CTC targets here, because the IRS geography and workbook sources currently ingested in this repo do not expose those component splits directly.

Validation

• uv run pytest tests/unit/calibration/test_ctc_diagnostics.py tests/unit/calibration/test_validate_national_h5.py tests/unit/calibration/test_target_config.py tests/unit/test_etl_irs_soi_overlay.py
• uv run pytest tests/unit/test_schema_views_and_lookups.py tests/unit/calibration/test_unified_matrix_builder.py
• uv run ruff check changelog.d/719.added.md policyengine_us_data/calibration/ctc_diagnostics.py policyengine_us_data/calibration/validate_national_h5.py policyengine_us_data/db/etl_irs_soi.py tests/unit/calibration/test_ctc_diagnostics.py tests/unit/calibration/test_validate_national_h5.py tests/unit/calibration/test_target_config.py tests/unit/test_etl_irs_soi_overlay.py
• uv run towncrier check --compare-with origin/main

[vercel]

@MaxGhenis is attempting to deploy a commit to the PolicyEngine Team on Vercel.

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[MaxGhenis]

Superseded by #721, which uses a branch in PolicyEngine/policyengine-us-data so CI can run past the check-fork gate.