Refactor the website around a Typst-backed reduction graph

[isPANN]

Stack

Depends on #1151. The base is refactor/reduction-contracts-clean; this PR contains only the website refactor on top of that branch.

Summary

• Make Graph a primary destination with problem/rule navigation, exact-variant selection, organic layouts, readable labels, and a persistent resizable inspector.
• Share Typst definitions, examples, proofs, and references between Graph and Atlas while preserving PDF export and family-level fallback for variants.
• Unify navigation, implementation/API/PDF links, typography, and Docs sidebar behavior; remove the superseded graph page.
• Load registry details and layout code on demand, bound article caching, and batch graph initialization.
• Validate exported HTML, apply CSP and release-specific asset URLs, restrict deployment permissions, verify downloaded tools, and gate publication on browser/build checks.

Verification

• 42 local browser tests passed using Chrome, including responsive layouts, graph interactions, variant links, cache eviction, and CSP enforcement.
• Docs and rustdoc search checks passed under CSP.
• Build-security unit tests and reduction graph JavaScript tests passed.
• npm audit reported zero vulnerabilities; git diff checks passed.
• Local mdBook, Typst HTML/PDF, and rustdoc assembly succeeded.
• Cold-load resource totals fell from approximately 1.02 MB to 0.31 MB for Home and 1.83 MB to 0.75 MB for Graph. Under local throttling, the longest measured Graph task fell from 211 ms to 86 ms; these are lab measurements, not production field metrics.

Remote CI and coverage remain to be verified. This PR does not deploy or merge the site.