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/serializers.py

@@ -1,11 +1,14 @@
 from rest_framework import serializers
-from .models import Person, Foerderung
+
+from .models import Foerderung, Person
+
 
 class PersonSerializer(serializers.ModelSerializer):
     class Meta:
         model = Person
         fields = "__all__"
 
+
 class FoerderungSerializer(serializers.ModelSerializer):
     class Meta:
         model = Foerderung