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/@testing-library/jest-dom/dist/index.js

@@ -0,0 +1,11 @@
+'use strict';
+
+var matchers = require('./matchers-98b869c1.js');
+require('redent');
+require('@adobe/css-tools');
+require('dom-accessibility-api');
+require('aria-query');
+require('picocolors');
+require('css.escape');
+
+expect.extend(matchers.extensions);