feat(fullscreen): track name on top, large & bold; artist name below, small

Swap DOM order and styles in the info cluster:
- fs-track-title: clamp(28px,4.5vw,68px) / weight 900 / var(--accent) — primary
- fs-artist-name: clamp(13px,1.5vw,22px) / weight 400 / 55% opacity — secondary
- fs-cluster gap: 12px → 8px (denser hierarchy)
- fs-meta: margin-top: 4px for breathing room after artist name

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/components/FullscreenPlayer.tsx

@@ -392,12 +392,12 @@ export default function FullscreenPlayer({ onClose }: FullscreenPlayerProps) {
           <FsArt fetchUrl={artUrl} cacheKey={artKey} />
         </div>
 
-        {/* Artist — massive statement */}
-        <p className="fs-artist-name">{currentTrack?.artist ?? '—'}</p>
-
-        {/* Track title — accent, light weight */}
+        {/* Track title — massive statement */}
         <p className="fs-track-title">{currentTrack?.title ?? '—'}</p>
 
+        {/* Artist — secondary, below track */}
+        <p className="fs-artist-name">{currentTrack?.artist ?? '—'}</p>
+
         {/* Metadata row */}
         {metaParts.length > 0 && (
           <div className="fs-meta">