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>

members/rules.py

@@ -6,4 +6,4 @@ from django.contrib.auth.models import AbstractUser
 
 @rules.predicate
 def is_member_manager(user: Optional[AbstractUser]) -> bool:
-    return user.has_perm('members.member_manager')
+    return user.has_perm("members.member_manager")