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/0018_destinataer_vierteljaehrlicher_betrag.py

@@ -6,13 +6,19 @@ from django.db import migrations, models
 class Migration(migrations.Migration):
 
     dependencies = [
-        ('stiftung', '0017_destinataer_haushaltsgroesse_and_more'),
+        ("stiftung", "0017_destinataer_haushaltsgroesse_and_more"),
     ]
 
     operations = [
         migrations.AddField(
-            model_name='destinataer',
-            name='vierteljaehrlicher_betrag',
-            field=models.DecimalField(blank=True, decimal_places=2, max_digits=12, null=True, verbose_name='Vierteljährlicher Betrag (€)'),
+            model_name="destinataer",
+            name="vierteljaehrlicher_betrag",
+            field=models.DecimalField(
+                blank=True,
+                decimal_places=2,
+                max_digits=12,
+                null=True,
+                verbose_name="Vierteljährlicher Betrag (€)",
+            ),
         ),
     ]