Validate redacted score-results sink policies

[ting-hong-shieh]

Summary

• document the results-sink policy pair semantics and the public 9.99 redaction sentinel
• validate policy tables, head names, numeric finiteness, ranges, and sentinel consistency at load time
• warn when a policy contains redacted fields and explicitly disable affected lanes
• add focused tests for valid, malformed, and redacted policies

Why

The checked-in public policy uses 9.99 to represent redacted thresholds. The cusp lane previously evaluated tau - cusp_delta; with the public values, 9.99 - 9.99 becomes 0. That arithmetic meant the sentinel did not reliably keep the lane disabled.

This change gives the sentinel explicit runtime behavior instead of relying on out-of-range comparisons. It does not propose, infer, or expose production threshold values.

Validation

• 42 passed, 3 skipped in bdsm/tests
• Ruff format check passed
• Ruff core error and import checks passed
• git diff --check passed

Addresses #25