A pure-CSS row of pulsing vertical bars (sinusoid-derived heights, staggered animation) that doubles as an active audio-processing indicator and an idle empty-state. Supports agent-state modes (connecting/listening/thinking/speaking), record/playback-scrub modes, and a live-volume mode that scales amplitude from a callback — decoupling the visual from the audio source. Ships its keyframe inline so it animates standalone after install.