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_invoices.py

@@ -25,7 +25,7 @@ def _client(user):
 class InvoiceTests(TestCase):
     def setUp(self):
         cache.clear()
-        self.user = User.objects.create(phone='09120007001', is_guest=False)
+        self.user = User.objects.create(phone='09120007001')
         self.client = _client(self.user)
         self.plan = Plan.objects.create(title='سالانه', price=299000, duration_days=365)
 
@@ -80,7 +80,7 @@ class InvoiceTests(TestCase):
 
     def test_someone_else_sees_nothing(self):
         self.buy()
-        stranger = User.objects.create(phone='09120007002', is_guest=False)
+        stranger = User.objects.create(phone='09120007002')
         self.assertEqual(self.invoices(_client(stranger)), [])
 
     def test_orders_from_before_the_snapshot_have_no_list_price(self):