fix: Improve rights management exception handling

- Add fallback permission object when Permission.DoesNotExist
- Create proper display name from field_name for missing permissions
- Prevents raw Django field objects from being displayed in template

app/stiftung/forms.py

@@ -1423,8 +1423,14 @@ class UserPermissionForm(forms.Form):
                             (field_name, field, permission)
                         )
                 except Permission.DoesNotExist:
-                    # Fallback for permissions that don't exist
-                    groups["system"]["permissions"].append((field_name, field, None))
+                    # Create a fallback permission-like object with proper display
+                    class FallbackPermission:
+                        def __init__(self, field_name):
+                            self.name = field_name.replace('_', ' ').title()
+                            self.codename = field_name
+                    
+                    fallback_perm = FallbackPermission(field_name)
+                    groups["system"]["permissions"].append((field_name, field, fallback_perm))
 
         return groups