Add settings page for managing forecasting API key and URL via UI

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

frontend/node_modules/workbox-routing/utils/getOrCreateDefaultRouter.js

@@ -0,0 +1,26 @@
+/*
+  Copyright 2019 Google LLC
+
+  Use of this source code is governed by an MIT-style
+  license that can be found in the LICENSE file or at
+  https://opensource.org/licenses/MIT.
+*/
+import { Router } from '../Router.js';
+import '../_version.js';
+let defaultRouter;
+/**
+ * Creates a new, singleton Router instance if one does not exist. If one
+ * does already exist, that instance is returned.
+ *
+ * @private
+ * @return {Router}
+ */
+export const getOrCreateDefaultRouter = () => {
+    if (!defaultRouter) {
+        defaultRouter = new Router();
+        // The helpers that use the default Router assume these listeners exist.
+        defaultRouter.addFetchListener();
+        defaultRouter.addCacheListener();
+    }
+    return defaultRouter;
+};