Add registry and results pages with cross-navigation

[nibzard]

Summary

• add the benchmark registry, benchmark results page, and supporting SEO/structured-data updates
• expand benchmark coverage and navigation across leaderboard, registry, and results views
• refine the results route and cross-link benchmarks back to their registry detail pages

Notes

• this branch is currently 19 commits ahead of steel-dev/main as of 2026-03-16
• local untracked directories docs/research and scripts were not included

Testing

• npm run build

[vercel]

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