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/dom-helpers/cjs/isDocument.js

@@ -0,0 +1,10 @@
+"use strict";
+
+exports.__esModule = true;
+exports.default = isDocument;
+
+function isDocument(element) {
+  return 'nodeType' in element && element.nodeType === document.DOCUMENT_NODE;
+}
+
+module.exports = exports["default"];