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/_mapToArray.js

@@ -0,0 +1,18 @@
+/**
+ * Converts `map` to its key-value pairs.
+ *
+ * @private
+ * @param {Object} map The map to convert.
+ * @returns {Array} Returns the key-value pairs.
+ */
+function mapToArray(map) {
+  var index = -1,
+      result = Array(map.size);
+
+  map.forEach(function(value, key) {
+    result[++index] = [key, value];
+  });
+  return result;
+}
+
+module.exports = mapToArray;