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/platform/browser/index.js

@@ -0,0 +1,13 @@
+import URLSearchParams from './classes/URLSearchParams.js';
+import FormData from './classes/FormData.js';
+import Blob from './classes/Blob.js';
+
+export default {
+  isBrowser: true,
+  classes: {
+    URLSearchParams,
+    FormData,
+    Blob,
+  },
+  protocols: ['http', 'https', 'file', 'blob', 'url', 'data'],
+};