Use value-only fiscal target loss weights

[MaxGhenis]

Summary

• remove ad hoc role/geography multipliers from US fiscal target loss weights
• weight rows only by target value within measure basis, normalized to mean 1
• write calibration diagnostics before hard release gates abort a failed build
• cover value-only weighting and failed-gate diagnostic metadata with focused tests

Local diagnostics

• Generated target-weight explorer: /Users/maxghenis/.codex/tmp/populace_target_weights_dashboard/index.html
• Generated target-weight CSV: /Users/maxghenis/.codex/tmp/populace_target_weights_dashboard/target_weights.csv

Tests

• uv run --frozen --all-packages --python 3.13 python -m pytest packages/populace-build/tests/test_us_fiscal_refresh_builder.py -q
• uv run --frozen --all-packages --python 3.13 python -m pytest packages/populace-calibrate/tests/test_solve.py packages/populace-build/tests/test_us_fiscal_refresh_builder.py packages/populace-build/tests/test_us_fiscal_targets.py -q
• uv run --frozen --all-packages --python 3.13 ruff check tools/build_us_fiscal_refresh_release.py packages/populace-build/tests/test_us_fiscal_refresh_builder.py
• git diff --check