Fix 3D camera interpolation and splat loading

[Sportinger]

Summary

• fix 3D video planes and nested scene rendering to use the active renderable scene camera
• add viewport progress for large Gaussian splat loading during fetch/read/parse/upload
• remove FPS look pitch cap and interpolate camera keyframes as world poses to avoid vertical-look fly-out arcs
• bump version to 1.5.10 and update changelog/docs

Checks

• npm run build
• npm run lint -- --quiet
• npm run test