fix(migrations): Skip data migration in test database

- Added check for :memory: and test in DB name
- Prevents calendar_app → django-scheduler migration from running during tests
- Test DB name: file:memorydb_default?mode=memory&cache=shared
- Saves ~10 seconds per test run and eliminates migration output spam

Previously showed ~80 lines of migration logs on every test run.

backend/calendar_app/migrations/0013_migrate_to_django_scheduler.py

@@ -16,6 +16,15 @@ def migrate_to_django_scheduler(apps, schema_editor):
     - Мигрирует события с конвертацией повторяемости
     - Мигрирует подписки в CalendarRelation
     """
+    # ВАЖНО: Пропускаем миграцию данных в тестовой БД
+    from django.conf import settings
+    db_name = settings.DATABASES['default']['NAME']
+    
+    # Проверяем признаки тестовой БД (SQLite :memory: или test_ prefix)
+    if ':memory' in str(db_name).lower() or 'test' in str(db_name).lower():
+        print("⏭️  Пропуск миграции данных в тестовой БД\n")
+        return
+    
     # ВАЖНО: Получаем ContentType через apps.get_model для миграций!
     ContentType = apps.get_model('contenttypes', 'ContentType')