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.d.ts

@@ -0,0 +1,10 @@
+import { Router } from '../Router.js';
+import '../_version.js';
+/**
+ * Creates a new, singleton Router instance if one does not exist. If one
+ * does already exist, that instance is returned.
+ *
+ * @private
+ * @return {Router}
+ */
+export declare const getOrCreateDefaultRouter: () => Router;