Preserve color through linear HDR bloom

[zackees]

What changed

• process source sampling, blur, and HDR bloom brackets in linear light using floating-point render targets
• preserve highlight-selection behavior while compositing the bloom brackets before the single sRGB output conversion
• declare BT.709/sRGB full-range color metadata in new RGB8 .fled recordings and decode RGB8 playback into linear light
• keep brightness limits perceptual and add focused color-space and capture tests

Why

Mapped renders were lifting dark shadows and shifting yellow midtones toward orange because blur and bloom mixed display-encoded 8-bit values. Repeated quantization also reduced useful highlight and shadow precision.

This keeps intermediate rendering linear and high precision, then quantizes once at the display/recording boundary. The result preserves deeper blacks, yellow midtones, highlight detail, and the established HDR bloom appearance.

Validation

• npm test — 712 tests passed
• npm run build — passed
• scoped ESLint over changed source/test files — passed
• npm run test:integration -- moviemaker-preview — passed
• focused moviemaker max-brightness GPU integration test — passed
• rendered 64×64, 60 fps comparison video inspected at the previously problematic 6 s and 10 s frames
• full FFmpeg decode of the output completed without errors