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/data/models/error_notebook_model.dart

@@ -20,7 +20,9 @@ class ErrorNotebookSummary {
   });
 
   factory ErrorNotebookSummary.fromJson(Map<String, dynamic> json) {
-    final rawBySubject = json['by_subject'] as Map<String, dynamic>? ?? {};
+    final rawBySubject = json['by_subject'] is Map
+        ? Map<String, dynamic>.from(json['by_subject'] as Map)
+        : <String, dynamic>{};
     final bySub = <String, int>{};
     rawBySubject.forEach((k, v) {
       bySub[k] = (v is num) ? v.toInt() : 0;

apps/student_app/lib/data/repositories/app_repositories.dart

@@ -119,6 +119,27 @@ class AuthRepository {
     throw ApiException('فشل استكمال فتح الملف الأكاديمي');
   }
 
+  Future<UserModel> updateStudentGrade(String gradeLevel, {String stream = 'general'}) async {
+    final res = await _api.post(
+      '/api/student/profile/update-grade',
+      body: {
+        'grade_level': gradeLevel,
+        'stream': stream,
+      },
+      requiresAuth: true,
+    );
+
+    if (res is Map<String, dynamic> && res['data'] != null) {
+      final data = res['data'];
+      if (data['user'] != null) {
+        final user = UserModel.fromJson(Map<String, dynamic>.from(data['user']));
+        await _storage.saveUser(user);
+        return user;
+      }
+    }
+    throw ApiException('فشل تحديث الصف الدراسي');
+  }
+
   Future<UserModel?> getMe() async {
     try {
       final res = await _api.get(AppConfig.meEndpoint);