XY-1120: [ELF AMK P6] Complete public quantitative competitor scoreboard and scoring report

[yvette-carlisle]

Summary

• Add the public quantitative competitor scoreboard contract, runner output, and checked-in June 27 evidence snapshot.
• Publish row-level ELF and competitor scoring with typed non-pass/blocker provenance and no universal leaderboard claim.
• Add the repo-native quantitative scoreboard task and docs/spec/evidence routing updates.

Validation

• cargo make fmt
• cargo make lint-fix
• cargo make checks
• cargo make real-world-memory-quantitative-scoreboard

Review

• Decodex independent fresh-context review checkpoint: clean for HEAD bc98c2f.