[Patch] Composite material emissive in the TBDR light pass

[miogds]

Split out of #1110 as requested, so the emissive question can be reviewed on its own.

What

The TBDR deferred light pass reads the G-buffer emissive but zeroes it before the final composite:

// set emissive to zero for now - need  to revisit this
emissive = 0.0;
float3 finalRGB = (float3)color.diff + color.spec + indirectLighting + emissive;

This removes the zeroing so material.emissiveValue written by the model pass actually reaches the screen. Kernels regenerated with buildkernels.sh.

Why it should be safe

• Material.emissiveValue defaults to .zero, the native-format loader defaults emissiveFactor to zero, and the MDL/usdz import path never sets it — so existing assets render identically. Only entities that explicitly call updateMaterialEmmisive (or the scene-builder .emissive() modifier from Scene builder DSL: primitive, light, and camera nodes + TBDR emissive fix #1110) change appearance.
• The non-TBDR fragmentLightShader path is untouched.

Testing

Verified on macOS with small emissive marker spheres orbiting a PBR-textured cube (dark IBL, no directional light): before, the spheres rendered black on their unlit side; after, they glow with their emissive color. Non-emissive geometry in the same scene (the PBR cube, textured meshes) renders unchanged before/after.

I know emissive was zeroed over a bug you found — if you remember its shape, happy to try to reproduce it against this change; and if you'd rather fix it your own way, feel free to treat this PR as a reference and close it.