Harden mesh imports and refresh shadow docs

[agustin-littlehat]

Summary

• Harden glTF, OBJ, and VOX import edge cases with parser coverage and compat-hunter warning handling.
• Update shadow render stats and cross-renderer shadow documentation for SVG shadow surfaces.
• Add border-shape benchmark variants and expand website API docs, including Fonts API.

Tests

• pnpm test
• pnpm build