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/siblings.js

@@ -0,0 +1,10 @@
+import collectSiblings from './collectSiblings';
+/**
+ * Collects all previous and next sibling elements of a given element.
+ * 
+ * @param node the element
+ */
+
+export default function siblings(node) {
+  return collectSiblings(node && node.parentElement ? node.parentElement.firstElementChild : null, node);
+}