Auto-select first tab

aleksis/apps/lesrooster/frontend/components/timetable_management/TimetableManagement.vue

@@ -63,7 +63,7 @@ export default defineComponent({
       selectedObjectType: null,
       selectedObjectTitle: "",
       selectedObjectDialogOpen: false,
-      selectedObjectDialogTab: null,
+      selectedObjectDialogTab: 0,
       timeGrids: [],
       groups: [],
       selectedGroup: null,