Add Viewer.js library and update asset URLs in history sidebar

web/history_sidebar.js

@@ -20,10 +20,8 @@ function ensureStylesheet() {
   document.head.appendChild(link);
 }
 
-const VIEWERJS_VERSION = "1.11.6";
-const VIEWERJS_BASE_URL = `https://cdn.jsdelivr.net/npm/viewerjs@${VIEWERJS_VERSION}/dist`;
-const VIEWERJS_CSS_URL = `${VIEWERJS_BASE_URL}/viewer.min.css`;
-const VIEWERJS_CORE_URL = `${VIEWERJS_BASE_URL}/viewer.min.js`;
+const VIEWER_CSS_URL = new URL("./vendor/viewerjs/viewer.min.css", import.meta.url).href;
+const VIEWER_JS_URL = new URL("./vendor/viewerjs/viewer.min.js", import.meta.url).href;
 
 const externalAssetPromises = new Map();
 
@@ -109,8 +107,8 @@ let viewerLoader = null;
 async function ensureViewer() {
   if (viewerLoader) return viewerLoader;
   viewerLoader = (async () => {
-    await ensureExternalStylesheet(VIEWERJS_CSS_URL);
-    await ensureExternalScript(VIEWERJS_CORE_URL);
+    await ensureExternalStylesheet(VIEWER_CSS_URL);
+    await ensureExternalScript(VIEWER_JS_URL);
     if (typeof window.Viewer !== "function") {
       throw new Error("Viewer global was not found after loading assets.");
     }

web/vendor/viewerjs/LICENSE-viewerjs

@@ -0,0 +1,21 @@
+The MIT License (MIT)
+
+Copyright 2015-present Chen Fengyuan
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.