Add floating synced lyrics with picture-in-picture fallback

frontend/index.html

@@ -656,6 +656,7 @@
     <script src="settings-sections.js"></script>
     <script src="downloads.js"></script>
     <script src="party-dj.js"></script>
+    <script src="lyrics-window.js"></script>
     <script src="app.js"></script>
   </body>
 </html>