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/offsetParent.js

@@ -0,0 +1,17 @@
+import css from './css';
+import ownerDocument from './ownerDocument';
+
+var isHTMLElement = function isHTMLElement(e) {
+  return !!e && 'offsetParent' in e;
+};
+
+export default function offsetParent(node) {
+  var doc = ownerDocument(node);
+  var parent = node && node.offsetParent;
+
+  while (isHTMLElement(parent) && parent.nodeName !== 'HTML' && css(parent, 'position') === 'static') {
+    parent = parent.offsetParent;
+  }
+
+  return parent || doc.documentElement;
+}