Read a Bonsai data frame. Bonsai centroid coordinates
come from camera/video pipelines that use image (top-left) origin;
the reader reflects y so the returned aniframe is in the
conventional bottom_left origin. Bonsai workflows are
user-defined and the output CSV does not record video resolution,
so pass video_height to get an accurate flip — otherwise max(y)
is used as a fallback.