Function release_brush 

pub fn release_brush(paint: Paint) -> bool

Releases a brush the screen no longer uses, so the Renderer drops its copy.

Without this a screen whose gradients change (hover, animation, theme) grows the Renderer’s brush table for the life of the app. Returns false when paint is not a registered brush. Releasing one still drawn is the caller’s mistake and is reported by the Renderer as a protocol error, not a crash. Registering the same brush again afterwards gives a new id.