fix: load album art via fetch+blob to bypass WebEngine URL restrictions

Direct background-image URLs to external hosts are blocked in the
local WebEngineView context; fetch the image as a blob and convert
to data URL instead.

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

plugin/contents/ui/dancer.html

@@ -1053,15 +1053,29 @@ function applyTheme(rgb) {
 
 const albumArtEl = document.getElementById('albumArt');
 
+let lastArtUrl = '';
+
+function setAlbumArt(url) {
+  if (!url || url === lastArtUrl) return;
+  lastArtUrl = url;
+  fetch(url)
+    .then(r => r.blob())
+    .then(blob => {
+      const reader = new FileReader();
+      reader.onload = () => {
+        albumArtEl.style.backgroundImage = `url('${reader.result}')`;
+      };
+      reader.readAsDataURL(blob);
+    })
+    .catch(() => {});
+}
+
 function fetchTheme() {
   fetch('http://127.0.0.1:8765/current')
     .then(r => r.json())
     .then(d => {
       if (d.rgb) applyTheme(d.rgb);
-      if (d.art_url) {
+      if (d.art_url) setAlbumArt(d.art_url);
-        albumArtEl.style.backgroundImage = `url('${d.art_url}')`;
-        albumArtEl.style.opacity = '1';
-      }
     })
     .catch(() => {});
 }