Renders an SVG countdown ring that depletes as numbers 3, 2, 1 count down, followed by a 'GO!' pop using spring() scale. The ring uses stroke-dasharray that reduces per second, driven by useCurrentFrame() and Math.floor().
Countdown start, ring colors, and GO text are configurable. A focused, minimal countdown scene that builds anticipation — suited for race starts, challenge videos, tutorial openings, or any content that benefits from a dramatic lead-in.