feat: add cover art to queue panel, remove redundant sidebar queue nav item

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

styles.css

@@ -295,6 +295,8 @@ nav{flex:1;overflow-y:auto;padding:4px 10px}
 .queue-item.active{background:var(--accent-dim)}
 .queue-item.active .qi-title{color:var(--accent)}
 .qi-idx{font-size:10px;color:var(--text3);width:16px;text-align:center;flex-shrink:0;font-family:var(--mono)}
+.qi-art{width:34px;height:34px;border-radius:5px;overflow:hidden;background:var(--surface2);flex-shrink:0;display:flex;align-items:center;justify-content:center;font-size:14px;color:var(--text3)}
+.qi-art img{width:100%;height:100%;object-fit:cover}
 .qi-info{flex:1;min-width:0}
 .qi-title{font-size:12px;font-weight:500;white-space:nowrap;overflow:hidden;text-overflow:ellipsis}
 .qi-artist{font-size:10px;color:var(--text2)}