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/@babel/runtime/helpers/assertThisInitialized.js

@@ -0,0 +1,5 @@
+function _assertThisInitialized(e) {
+  if (void 0 === e) throw new ReferenceError("this hasn't been initialised - super() hasn't been called");
+  return e;
+}
+module.exports = _assertThisInitialized, module.exports.__esModule = true, module.exports["default"] = module.exports;