docs(morph): add interactive cube-to-sphere example

[alowpoly]

Summary

• align the Morph README and website guide around the published package
• add a rendered 768-polygon cube-to-sphere and swirl example with retained DOM leaves, sliders, and orbit controls
• ship the prepared model, lighting states, and browser triangle fallback assets with the docs

Validation

• pnpm test
• pnpm build
• pnpm build:website
• Chrome: verified cube framing, slider deformation, and drag-to-orbit on /guides/morph/