release: 1.5.7

[Sportinger]

Summary

• bound the prepared gaussian splat runtime cache so precise export no longer retains every full frame runtime in memory
• keep the export fallback for oversized Three.js splat runtime preparation instead of crashing the browser
• bump APP_VERSION to 1.5.7 and add the release changelog entry

Validation

• npm run build
• npm run lint
• npm run test