Fix Sylva Living World font loading in sandbox

[Vaishnavi220506]

Summary

• Fixes SylvaLivingWorldScene: bundled font 404s via CORS in its own sandboxed iframe (sourceUrl/assetBaseUrl not exposed) #39 by inlining the Lexend font into SylvaLivingWorldScene, removing the sandboxed iframe's cross-origin font request.
• Adds a configurable, normalized assetBaseUrl for any remaining relative scene assets while keeping the iframe sandbox at allow-scripts only.
• Makes the community sync preserve the font and generated fix, with regression coverage.
• Keeps the existing package checks portable on Windows (POSIX install paths, line-ending-stable snapshots, and npm smoke execution).

Validation

• npm run build
• npm run smoke:package
• npm test (29 passing)
• npm run typecheck
• npm run build:site
• npm run build:lib

The local build and package smoke test pass.