Add state income tax calibration targets from Census STC

[MaxGhenis]

Summary

• Adds ETL pipeline for state-level individual income tax collections from Census Bureau's Annual Survey of State Government Tax Collections (STC)
• Uses hardcoded FY2023 data for all 50 states + DC ($531B total)
• Creates calibration targets using stratum_group_id 7 for state income tax

Supersedes #493 (rebased onto main; original targeted stale db-work branch).

Test plan

• Run make database to verify ETL executes successfully
• Check database contains state income tax strata and targets
• Verify validation passes (state_income_tax variable exists in policyengine-us)

Closes #492

🤖 Generated with Claude Code

[MaxGhenis]

Reviewed. CI passes, code structure is clean.

⚠️ Data accuracy concern: The hardcoded FY2023 values may not match Census STC. Spot-checking via FRED (CAINCTAX, NYINCTAX):

• CA: PR has $115.8B, FRED shows $96.4B for FY2023
• NY: PR has $63.2B, FRED shows $58.8B for FY2023

This could be a vintage/table mismatch (STC Table 1 vs FRED series), or the PR values may be from a different fiscal year. Since this is database-only (not consumed by build_loss_matrix() yet), there's no production impact, but the values should be verified against the actual Census STC download before this feeds into calibration.

Otherwise ready to merge.