Drop the --player-height bottom inset so the fixed visualizer fills the
viewport; the inset player bar no longer leaves a page-background gap. The
spacer now occludes via opaque page-surface + z-index. Visualizer no longer
reads --player-height, so spacer.ts coalescing is removed.
Replace the 20 synthetic bars with a contained WaveformVisualizer driven by the live player, pointed at the current track; add a Fill mode (CSS-only, defaults off) sizing the canvas to its container; place the lava-lamp icon to popover on the card.