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/@nodelib/fs.stat/out/providers/async.d.ts

@@ -0,0 +1,4 @@
+import type Settings from '../settings';
+import type { ErrnoException, Stats } from '../types';
+export declare type AsyncCallback = (error: ErrnoException, stats: Stats) => void;
+export declare function read(path: string, settings: Settings, callback: AsyncCallback): void;