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/dom-helpers/esm/camelizeStyle.js

@@ -0,0 +1,10 @@
+/**
+ * Copyright 2014-2015, Facebook, Inc.
+ * All rights reserved.
+ * https://github.com/facebook/react/blob/2aeb8a2a6beb00617a4217f7f8284924fa2ad819/src/vendor/core/camelizeStyleName.js
+ */
+import camelize from './camelize';
+var msPattern = /^-ms-/;
+export default function camelizeStyleName(string) {
+  return camelize(string.replace(msPattern, 'ms-'));
+}