feat(useragent): callouts feature for approving new things

useragent/lib/features/callouts/active_callout.dart

@@ -0,0 +1,16 @@
+import 'package:arbiter/features/callouts/callout_event.dart';
+import 'package:freezed_annotation/freezed_annotation.dart';
+
+part 'active_callout.freezed.dart';
+
+@freezed
+abstract class ActiveCallout with _$ActiveCallout {
+  const factory ActiveCallout({
+    required String id,
+    required String title,
+    required String description,
+    String? iconUrl,
+    required DateTime addedAt,
+    required CalloutData data,
+  }) = _ActiveCallout;
+}