style(ui): Spotify-like palette, player, sidebar and dashboard polish
- Dark palette: background 0.11, card 0.14, sidebar 0.08 (Spotify #121212 feel)
- MiniPlayer: h-16, thinner progress bar, compact cover/times, rounded actions
- Sidebar: minimal header, lighter section labels, clean nav hover (no heavy border)
- Header: h-16, rounded search pill, compact user pill and dropdown
- Dashboard: pt-20 to match header, StatCard typography and spacing tweaks
- Visual: register-page snapshot + small maxDiffPixels tolerance for font variance
Co-authored-by: Cursor <cursoragent@cursor.com>
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