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/lodash/_getHolder.js

@@ -0,0 +1,13 @@
+/**
+ * Gets the argument placeholder value for `func`.
+ *
+ * @private
+ * @param {Function} func The function to inspect.
+ * @returns {*} Returns the placeholder value.
+ */
+function getHolder(func) {
+  var object = func;
+  return object.placeholder;
+}
+
+module.exports = getHolder;