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/cancel/CanceledError.js

@@ -0,0 +1,22 @@
+'use strict';
+
+import AxiosError from '../core/AxiosError.js';
+
+class CanceledError extends AxiosError {
+  /**
+   * A `CanceledError` is an object that is thrown when an operation is canceled.
+   *
+   * @param {string=} message The message.
+   * @param {Object=} config The config.
+   * @param {Object=} request The request.
+   *
+   * @returns {CanceledError} The created error.
+   */
+  constructor(message, config, request) {
+    super(message == null ? 'canceled' : message, AxiosError.ERR_CANCELED, config, request);
+    this.name = 'CanceledError';
+    this.__CANCEL__ = true;
+  }
+}
+
+export default CanceledError;