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.

clubmanager/base.py

@@ -0,0 +1,21 @@
+import uuid
+
+from django.db import models
+
+
+class UUIDModel(models.Model):
+    """Abstract base class giving every model a UUID primary key"""
+
+    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
+
+    class Meta:
+        abstract = True
+
+
+class ClubScopedModel(UUIDModel):
+    """Abstract base for entities owned by a single club (tenant root)."""
+
+    club = models.ForeignKey("club.Club", on_delete=models.CASCADE, related_name="%(class)ss")
+
+    class Meta:
+        abstract = True