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/signal-exit/dist/cjs/browser.d.ts

@@ -0,0 +1,12 @@
+/**
+ * This is a browser shim that provides the same functional interface
+ * as the main node export, but it does nothing.
+ * @module
+ */
+import type { Handler } from './index.js';
+export declare const onExit: (cb: Handler, opts: {
+    alwaysLast?: boolean;
+}) => () => void;
+export declare const load: () => void;
+export declare const unload: () => void;
+//# sourceMappingURL=browser.d.ts.map