Add an incremental SHA-256 library for the browser and node tests

frontend/index.html

@@ -561,6 +561,7 @@
     <script src="video-edit.js"></script>
     <script src="lyrics-core.js"></script>
     <script src="stats-core.js"></script>
+    <script src="sha256.js"></script>
     <script src="async-guard.js"></script>
     <script src="sw-update.js"></script>
     <script src="app.js"></script>