[codex] Add surface contract fragments and safe artifact compiler

[nahiyankhan]

Summary

This branch carries the surface contract fragments work forward across the Summon stack:

• migrates the maintainer demo app to a React/Vite/Tailwind SPA with route-level pages for generate, batch, strict, fatal, adversarial, and fragment comparison flows
• updates the Surface Gallery presets/styling and keeps its public-package import boundary intact
• unifies surface planning around the agent broker and narrows host tool selection through policy-backed surface contracts
• moves Ghost steering to canonical fingerprint package roots and emits review metadata from the relay context
• adds a safe artifact HTML compiler path, including runtime validation, canonicalization, host/react/sandbox integration, and public package exports
• refreshes adoption/security/debugging docs for the new public package and sandbox behavior

Validation

• pnpm typecheck
• pnpm test
• pnpm build
• pnpm check:public-packages
• pnpm check:public-api
• pnpm smoke:public-packages
• pnpm test:gallery - 7 passed
• pnpm test:safety - 26 passed
• pnpm pack:dry-run
• git diff --check

Review Focus

Please pay closest attention to the public API exposure of compileArtifactHtml, the safe compiler and sandbox boundary changes, the Ghost fingerprint package integration, and the broad demo/gallery route migration.