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/height.js

@@ -0,0 +1,13 @@
+import getWindow from './isWindow';
+import offset from './offset';
+/**
+ * Returns the height of a given element.
+ * 
+ * @param node the element
+ * @param client whether to use `clientHeight` if possible
+ */
+
+export default function height(node, client) {
+  var win = getWindow(node);
+  return win ? win.innerHeight : client ? node.clientHeight : offset(node).height;
+}