🚨(backend) fix linter warnings

Recent updates of dev/ruff and dev/pylint dependencies led
to new linting warnings.

Pylint 3.2.0 introduced a new check `possibly-used-before-assignment`,
which ensures variables are defined regardless of conditional statements.

Some if/else branches were missing defaults. These have been fixed.

src/backend/core/api/__init__.py

@@ -1,4 +1,5 @@
 """Meet core API endpoints"""
+
 from django.conf import settings
 from django.core.exceptions import ValidationError
 
@@ -22,6 +23,8 @@ def exception_handler(exc, context):
             detail = exc.message
         elif hasattr(exc, "messages"):
             detail = exc.messages
+        else:
+            detail = ""
 
         exc = drf_exceptions.ValidationError(detail=detail)
 

src/backend/core/api/permissions.py

@@ -1,4 +1,5 @@
 """Permission handlers for the Meet core app."""
+
 from rest_framework import permissions
 
 from ..models import RoleChoices

src/backend/core/api/serializers.py

@@ -1,4 +1,5 @@
 """Client serializers for the Meet core app."""
+
 from django.conf import settings
 from django.utils.translation import gettext_lazy as _
 

src/backend/core/api/viewsets.py

@@ -1,4 +1,5 @@
 """API endpoints"""
+
 import uuid
 
 from django.conf import settings