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>

notifications/tests.py

@@ -93,7 +93,7 @@ class NotificationListCapTests(TestCase):
     def setUp(self):
         cache.clear()
         self.client = APIClient()
-        self.user = User.objects.create(device_id='dev-notif-cap', is_guest=True, name='n')
+        self.user = User.objects.create(phone='09000000065', name='n')
         self.token = issue_access_token(self.user.id)
 
     def test_returns_at_most_100_newest_with_correct_unread_count(self):
@@ -120,7 +120,7 @@ class NotificationPayloadShapeTests(TestCase):
     def setUp(self):
         cache.clear()
         self.client = APIClient()
-        self.user = User.objects.create(device_id='dev-notif-shape', is_guest=True, name='n')
+        self.user = User.objects.create(phone='09000000066', name='n')
         self.token = issue_access_token(self.user.id)
 
     def test_list_item_carries_body_and_created_at(self):