refactor: load album art directly from http://127.0.0.1:8765/art

CORS is now fixed so img.src with http URL works. Remove temp file approach.

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

plugin/contents/ui/dancer.html

@@ -1068,7 +1068,7 @@ function fetchTheme() {
       if (d.art_url && d.art_url !== lastArtUrl) {
         lastArtUrl = d.art_url;
         document.getElementById('albumArtImg').src =
-          'file:///tmp/skeledance_art.jpg?' + Date.now();
+          'http://127.0.0.1:8765/art?' + Date.now();
       }
     })
     .catch(() => {});