Remove the guest system entirely: no is_guest/device_id, no guest throttles, phone login is the only way in

accounts.0008 drops the columns and refuses to run while guest rows exist.
Docs describe the current state; tests that only proved guest behaviour are gone.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

payment/tests_refund.py

@@ -27,7 +27,7 @@ from .services import OrderStateError, apply_order_payment_result, cancel_pendin
 class _Base(TestCase):
     def setUp(self):
         cache.clear()
-        self.user = User.objects.create(phone='09120007401', is_guest=False)
+        self.user = User.objects.create(phone='09120007401')
         self.client_app = APIClient()
         self.client_app.credentials(HTTP_AUTHORIZATION=f'Bearer {issue_access_token(self.user.id)}')
         self.pack = Plan.objects.get(kind='pack', question_credits=20)
@@ -107,7 +107,7 @@ class RefundServiceTests(_Base):
         self.assertEqual(sub.status, 'canceled')
 
     def test_the_referrers_commission_for_this_order_is_undone(self):
-        referrer = User.objects.create(phone='09120007402', is_guest=False)
+        referrer = User.objects.create(phone='09120007402')
         account = AffiliateAccount.objects.create(user_id=referrer.id, referral_code='REF1', commission_rate=0.1)
         Conversion.objects.create(affiliate_account=account, referred_user_id=self.user.id)
         order = self.paid_pack()