Add household count target to ECPS calibration

[MaxGhenis]

Summary

• add a source household-count target to legacy ECPS calibration so reweighting cannot scale total household mass upward
• weight the household-count target like other hard national controls and require it before EnhancedCPS reweighting starts
• add fast regression tests for the target, target weighting, and clone-prior total preservation
• update policyengine-us to 1.711.0 so the freshness guard passes

Verification

• uv run python .github/scripts/check_policyengine_us_dependency.py --mode fail
• uv run towncrier check --compare-with upstream/main --staged
• uv run ruff check policyengine_us_data/utils/loss.py policyengine_us_data/datasets/cps/enhanced_cps.py policyengine_us_data/utils/init.py policyengine_us_data/utils/national_target_parity.py tests/unit/calibration/test_loss_targets.py tests/unit/datasets/test_enhanced_cps_seeding.py
• uv run pytest tests/unit/calibration/test_loss_targets.py tests/unit/datasets/test_enhanced_cps_seeding.py tests/unit/test_national_target_parity.py tests/unit/test_enhanced_cps.py
• local synthetic reweight check with nation/source/household_count target: final total 98.99 on target 100 after 75 epochs