Format code with Black and isort for CI/CD compliance

- Apply Black formatting to all Python files in core and stiftung modules
- Fix import statement ordering with isort
- Ensure all code meets automated quality standards
- Resolve CI/CD pipeline formatting failures
- Maintain consistent code style across the entire codebase

app/stiftung/migrations/0009_alter_dokumentlink_paperless_document_id.py

@@ -6,13 +6,13 @@ from django.db import migrations, models
 class Migration(migrations.Migration):
 
     dependencies = [
-        ('stiftung', '0008_dokumentlink_destinataer_id_and_more'),
+        ("stiftung", "0008_dokumentlink_destinataer_id_and_more"),
     ]
 
     operations = [
         migrations.AlterField(
-            model_name='dokumentlink',
-            name='paperless_document_id',
+            model_name="dokumentlink",
+            name="paperless_document_id",
             field=models.IntegerField(),
         ),
     ]