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/at.js

@@ -0,0 +1,23 @@
+var baseAt = require('./_baseAt'),
+    flatRest = require('./_flatRest');
+
+/**
+ * Creates an array of values corresponding to `paths` of `object`.
+ *
+ * @static
+ * @memberOf _
+ * @since 1.0.0
+ * @category Object
+ * @param {Object} object The object to iterate over.
+ * @param {...(string|string[])} [paths] The property paths to pick.
+ * @returns {Array} Returns the picked values.
+ * @example
+ *
+ * var object = { 'a': [{ 'b': { 'c': 3 } }, 4] };
+ *
+ * _.at(object, ['a[0].b.c', 'a[1]']);
+ * // => [3, 4]
+ */
+var at = flatRest(baseAt);
+
+module.exports = at;