Fix student grade registration: set grade_10 as default, add auto-heal for legacy tawjihi_2008, add student grade selector and update-grade API

apps/student_app/lib/logic/cubits/auth_cubit.dart

@@ -169,6 +169,22 @@ class AuthCubit extends Cubit<AuthState> {
     }
   }
 
+  Future<void> updateGrade(String gradeLevel, {String stream = 'general'}) async {
+    final currentState = state;
+    if (currentState is! Authenticated) return;
+    AppLogger.log('Updating student grade to $gradeLevel ($stream)...', tag: 'AUTH_CUBIT');
+    emit(AuthLoading());
+    try {
+      final updatedUser = await _authRepo.updateStudentGrade(gradeLevel, stream: stream);
+      AppLogger.log('Grade updated successfully -> ${updatedUser.gradeLevel}', tag: 'AUTH_CUBIT');
+      emit(Authenticated(user: updatedUser, activeRole: 'student'));
+    } catch (e) {
+      AppLogger.error('Update Grade Exception', error: e, tag: 'AUTH_CUBIT');
+      emit(AuthError(e.toString()));
+      emit(currentState);
+    }
+  }
+
   Future<void> switchRole(String newRole) async {
     final currentState = state;
     if (currentState is Authenticated) {

apps/student_app/lib/logic/cubits/video_playback_cubit.dart

@@ -93,7 +93,8 @@ class VideoPlaybackCubit extends Cubit<VideoPlaybackState> {
     final storageKey = _getLessonStorageKey(lesson);
 
     try {
-      var playback = await _repo.getLessonPlayback(lesson.markdownFilePath ?? lesson.id, subjectId: subject?.id);
+      final cleanKey = (lesson.markdownFilePath ?? lesson.id).replaceAll(RegExp(r'\.md$'), '');
+      var playback = await _repo.getLessonPlayback(cleanKey, subjectId: subject?.id);
       if (playback.videoUrl.isEmpty) {
         throw StateError('لم يربط الخادم فيديو R2 بهذا الدرس بعد.');
       }