colorGrade post-process shader

Brightness, saturation and contrast as multipliers around an identity of 1.0. pp.add(name, "colorGrade", { brightness = 1.1, saturation = 0.8 }) registers it, and asset.resolve("@builtin::shaders.post.colorGrade", "shader"):getProperties() reads the knobs below before it is added.

The three run in that order on the sampled frame: brightness scales the colour, saturation mixes it against its own Rec. 709 luminance, and contrast pushes it away from mid grey. Each is a multiplier, so 1.0 leaves the frame as it was and all three at 1.0 pass it through unchanged.

color_correction grades the same three quantities as ADDITIVE offsets around 0.0 and adds a tint colour, so a look authored for one does not transfer to the other by copying its numbers.

Property	Meaning
brightness	Multiplies the colour.
saturation	0 is luminance alone, 1 is the frame's own colour.
contrast	Scales distance from mid grey.