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.scandir/out/providers/async.d.ts

@@ -0,0 +1,7 @@
+/// <reference types="node" />
+import type Settings from '../settings';
+import type { Entry } from '../types';
+export declare type AsyncCallback = (error: NodeJS.ErrnoException, entries: Entry[]) => void;
+export declare function read(directory: string, settings: Settings, callback: AsyncCallback): void;
+export declare function readdirWithFileTypes(directory: string, settings: Settings, callback: AsyncCallback): void;
+export declare function readdir(directory: string, settings: Settings, callback: AsyncCallback): void;