Refactor accounts app into authentication and club apps

- Split the accounts app into new authentication and club apps for better separation of concerns.
- Migrate the custom User, Member, and Family models to the authentication app.
- Introduce Club and ClubMembership models in the club app.
- Refactor Family model to use UUID as the primary key and consolidate family-role relationships into a new FamilyMembership model.
- Update tests, managers, and migrations to align with the new structure.

authentication/managers.py

@@ -0,0 +1,32 @@
+from django.contrib.auth.base_user import BaseUserManager
+
+
+class UserManager(BaseUserManager):
+    """Manager for the email-based custom User model."""
+
+    use_in_migrations = True
+
+    def _create_user(self, email, password, **extra_fields):
+        if not email:
+            raise ValueError("Users must have an email address.")
+        email = self.normalize_email(email)
+        user = self.model(email=email, **extra_fields)
+        user.set_password(password)
+        user.save(using=self._db)
+        return user
+
+    def create_user(self, email, password=None, **extra_fields):
+        extra_fields.setdefault("is_staff", False)
+        extra_fields.setdefault("is_superuser", False)
+        return self._create_user(email, password, **extra_fields)
+
+    def create_superuser(self, email, password=None, **extra_fields):
+        extra_fields.setdefault("is_staff", True)
+        extra_fields.setdefault("is_superuser", True)
+
+        if extra_fields.get("is_staff") is not True:
+            raise ValueError("Superuser must have is_staff=True.")
+        if extra_fields.get("is_superuser") is not True:
+            raise ValueError("Superuser must have is_superuser=True.")
+
+        return self._create_user(email, password, **extra_fields)