feat(frontend): add API client, layout, and routing

- Create Axios-based API client with sources, jobs, and dashboard endpoints
- Add responsive Layout component with navigation sidebar
- Set up React Router with Dashboard, Backups, and Settings routes
- Configure TanStack Query provider with default options
- Use lucide-react for navigation icons

frontend/node_modules/react-router-dom/dist/main.js

@@ -0,0 +1,19 @@
+/**
+ * React Router DOM v6.30.3
+ *
+ * Copyright (c) Remix Software Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE.md file in the root directory of this source tree.
+ *
+ * @license MIT
+ */
+'use strict';
+
+/* eslint-env node */
+
+if (process.env.NODE_ENV === "production") {
+  module.exports = require("./umd/react-router-dom.production.min.js");
+} else {
+  module.exports = require("./umd/react-router-dom.development.js");
+}