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/react-transition-group/cjs/utils/reflow.js

@@ -0,0 +1,10 @@
+"use strict";
+
+exports.__esModule = true;
+exports.forceReflow = void 0;
+
+var forceReflow = function forceReflow(node) {
+  return node.scrollTop;
+};
+
+exports.forceReflow = forceReflow;