implemented a comprehensive client-side demo mode triggered by a "demo@" username prefix, serving curated fixture data for all app modules

lib/state/app/modules/grade_averages/bloc/grade_averages_bloc.dart

@@ -1,15 +1,19 @@
 import 'package:hydrated_bloc/hydrated_bloc.dart';
 
+import '../../../../../api/demo/demo_mode.dart';
 import 'grade_averages_event.dart';
 import 'grade_averages_state.dart';
 
 class GradeAveragesBloc
     extends HydratedBloc<GradeAveragesEvent, GradeAveragesState> {
+  // Seeded with a realistic spread in demo mode (average 2.0); empty otherwise.
+  static const List<int> _demoGrades = [1, 2, 2, 2, 3, 2, 1, 3, 2, 2];
+
   GradeAveragesBloc()
     : super(
-        const GradeAveragesState(
+        GradeAveragesState(
           gradingSystem: GradeAveragesGradingSystem.middleSchool,
-          grades: [],
+          grades: DemoMode.active ? _demoGrades : const [],
         ),
       ) {
     on<GradingSystemChanged>((event, emit) {