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/cjs/react.shared-subset.development.js

@@ -0,0 +1,20 @@
+/**
+ * @license React
+ * react.shared-subset.development.js
+ *
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+'use strict';
+
+if (process.env.NODE_ENV !== "production") {
+  (function() {
+'use strict';
+
+// eslint-disable-next-line react-internal/prod-error-codes
+throw new Error('This entry point is not yet supported outside of experimental channels');
+  })();
+}