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/esm/ownerWindow.js

@@ -0,0 +1,11 @@
+import ownerDocument from './ownerDocument';
+/**
+ * Returns the owner window of a given element.
+ * 
+ * @param node the element
+ */
+
+export default function ownerWindow(node) {
+  var doc = ownerDocument(node);
+  return doc && doc.defaultView || window;
+}