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/clear.js

@@ -0,0 +1,16 @@
+/**
+ * Removes all child nodes from a given node.
+ * 
+ * @param node the node to clear
+ */
+export default function clear(node) {
+  if (node) {
+    while (node.firstChild) {
+      node.removeChild(node.firstChild);
+    }
+
+    return node;
+  }
+
+  return null;
+}