Add CBO income tax receipts source package

[MaxGhenis]

Summary

• add a CBO February 2026 Historical Budget Data source package for federal individual income tax receipts
• emit the FY2024 CBO individual income tax receipts fact used by Populace as the macro income-tax calibration control
• assert consumer-fact lineage, direct workbook provenance, and FY2024 value 2.426067T in source-package tests

Validation

• uv run ruff check arch/source_package.py tests/test_arch_source_package.py
• uv run pytest tests/test_arch_source_package.py
• uv run arch build-bundle --year 2024 --source cbo-individual-income-tax-receipts-2026-02 --source jct-tax-expenditures-2024 --out artifacts/cbo_jct_bundle_2024 --replace