feat: show playlist description in detail view

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

styles.css

@@ -165,6 +165,7 @@ nav{flex:1;overflow-y:auto;padding:4px 10px}
 .album-artist-name{font-size:14px;color:var(--text2);margin-bottom:10px;cursor:pointer}
 .album-artist-name:hover{color:var(--accent)}
 .album-stats{font-size:12px;color:var(--text3)}
+.playlist-detail-desc{font-size:13px;color:var(--text2);line-height:1.5;margin-top:6px;max-width:480px}
 .album-actions{display:flex;gap:8px;margin-top:16px;flex-wrap:wrap}
 .btn-play-all{display:flex;align-items:center;gap:7px;padding:10px 20px;border-radius:25px;background:var(--accent);color:#000;border:none;font-family:var(--font);font-size:13px;font-weight:700;cursor:pointer;transition:opacity .15s,transform .15s}
 .btn-play-all:hover{opacity:.9;transform:scale(1.02)}