Infrastructure: Tier I/II/III aggregated scoring and weighting

## Description
Design and implement the overall scoring scheme that combines results across tiers.

## Open questions
- How to weight individual metrics within each tier
- How to combine Tier I pass/fail with Tier II continuous scores
- Treatment of extended vs core metrics in overall score
- Presentation format (leaderboard, radar plots, etc.)
- Whether Tier I failures should gate Tier II/III scoring entirely

## Notes
- This is a protocol-level design question that needs community input
- Start with a simple additive scheme and iterate

No files, tests, or entry points are named. Start by reviewing the existing tier metrics and scoring outputs, then gather community input on metric weights, tier combinations, extended versus core metrics, presentation, and gating. Done means an agreed protocol-level scoring scheme is documented and ready to implement.

Written by the indexing model from the issue text.