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/escalade/index.d.mts

@@ -0,0 +1,11 @@
+type Promisable<T> = T | Promise<T>;
+
+export type Callback = (
+	directory: string,
+	files: string[],
+) => Promisable<string | false | void>;
+
+export default function (
+	directory: string,
+	callback: Callback,
+): Promise<string | void>;