Apply ruff formatting and fix unused import linting errors

Remove unused imports flagged by ruff (F401), apply ruff format across all
files, and restore members.signals side-effect import with noqa: F401 so the
post_save signal that auto-creates Member profiles continues to fire.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/members/urls.py

@@ -1,4 +1,4 @@
-from django.urls import include, path
+from django.urls import path
 
 from .views import MemberAddView, MemberDeleteView, MemberEditView, MemberListView, MemberLoadView