show classname instead of teacher name in teacher timetable view

lib/widget_data/widget_data.dart

@@ -28,6 +28,9 @@ abstract class WidgetLesson with _$WidgetLesson {
     required String subjectShort,
     String? subjectLong,
     String? room,
+    /// On teacher accounts this carries the class label ("7a") instead of the
+    /// teacher short name — see `WidgetDataMapper` `showClassInsteadOfTeacher`;
+    /// [originalTeacher] is null in that case.
     String? teacher,
     String? originalTeacher,
     required WidgetLessonStatus status,