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/axios/lib/helpers/isAxiosError.js

@@ -0,0 +1,14 @@
+'use strict';
+
+import utils from '../utils.js';
+
+/**
+ * Determines whether the payload is an error thrown by Axios
+ *
+ * @param {*} payload The value to test
+ *
+ * @returns {boolean} True if the payload is an error thrown by Axios, otherwise false
+ */
+export default function isAxiosError(payload) {
+  return utils.isObject(payload) && payload.isAxiosError === true;
+}