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.js

@@ -0,0 +1,10 @@
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.unload = exports.load = exports.onExit = void 0;
+const onExit = () => () => { };
+exports.onExit = onExit;
+const load = () => { };
+exports.load = load;
+const unload = () => { };
+exports.unload = unload;
+//# sourceMappingURL=browser.js.map