Add JWT auth with per-user data isolation and account settings.

Users can register, log in, and manage profile/password in a personal account page; server data is scoped by owner across contacts, maps, tags, and import.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/core/access.py

@@ -0,0 +1,19 @@
+from django.conf import settings
+
+
+def use_jwt_auth():
+    return getattr(settings, 'USE_JWT_AUTH', False)
+
+
+def scope_by_owner(queryset, user, owner_field='owner'):
+    if not use_jwt_auth():
+        return queryset
+    if user and user.is_authenticated:
+        return queryset.filter(**{owner_field: user})
+    return queryset.none()
+
+
+def user_workspace_id(user):
+    if user and user.is_authenticated:
+        return str(user.pk)
+    return settings.DEFAULT_WORKSPACE_ID