feat(grade10): add chemistry, biology, and earth sciences virtual labs, fix video CDN playback, teacher submissions SQL, and enable authenticated lesson reading

apps/teacher_app/lib/logic/cubits/teacher_studio_cubit.dart

@@ -336,10 +336,19 @@ class TeacherStudioCubit extends Cubit<TeacherStudioState> {
       clearError: true,
     ));
     try {
-      final preflight = await repository.preflightSubmission(
+      var preflight = await repository.preflightSubmission(
         curriculumLessonId: selectedCurriculumLessonId!,
         idempotencyKey: _newIdempotencyKey(),
       );
+      if (preflight['status']?.toString() == 'existing_submission' && preflight['submission_id'] != null) {
+        // إذا كانت الحصة مسجلة مسبقاً، نطلب تلقائياً إنشاء نسخة مرشحة للاستبدال
+        preflight = await repository.preflightSubmission(
+          curriculumLessonId: selectedCurriculumLessonId!,
+          idempotencyKey: _newIdempotencyKey(),
+          replacement: true,
+          submissionId: preflight['submission_id'].toString(),
+        );
+      }
       if (preflight['status']?.toString() != 'ready_for_upload') {
         emit(state.copyWith(
           isAuditing: false,