OverlayPosition
data class OverlayPosition(val top: Double? = null, val bottom: Double? = null, val left: Double? = null, val right: Double? = null)
Position of an overlay ad within the player surface, as fractions 0.0-1.0 of the surface (mirrors the TS OverlayPosition). Only one of {top, bottom} and one of {left, right} is typically supplied; the renderer converts these to platform layout. Brain-agnostic — only the overlay renderer reads them.