feat: Add AppUserAccountActionShown event

- Tracks account action shown
- Updates user timestamp

Author: fulleni

lib/app/bloc/app_event.dart

@@ -99,3 +99,17 @@ class _AppConfigFetchRequested extends AppEvent {
   /// {@macro _app_config_fetch_requested}
   const _AppConfigFetchRequested();
 }
+
+/// {@template app_user_account_action_shown}
+/// Event triggered when an AccountAction has been shown to the user,
+/// prompting an update to their `lastAccountActionShownAt` timestamp.
+/// {@endtemplate}
+class AppUserAccountActionShown extends AppEvent {
+  /// {@macro app_user_account_action_shown}
+  const AppUserAccountActionShown({required this.userId});
+
+  final String userId;
+
+  @override
+  List<Object> get props => [userId];
+}