Replace blink-all transition with a circular ring buffer: each lyric
line is absolutely positioned (30px slot). On advance the ring scrolls
up, the outgoing element is recycled to the bottom with new content
(transition disabled for the snap). All style properties (top, opacity,
font-size, color, text-shadow) animate together via CSS transition so
the new active line gains focus as it scrolls into center position.
Jumps (seek / track change) still use a crossfade.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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