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>

accounts/tests_birth_date.py

@@ -47,7 +47,7 @@ class JalaliConversionTests(SimpleTestCase):
 class ProfileBirthDateApiTests(TestCase):
     def setUp(self):
         cache.clear()
-        self.user = User.objects.create(device_id='birth-date-device', is_guest=True)
+        self.user = User.objects.create(phone='09000000053')
         self.client = APIClient()
         self.client.credentials(HTTP_AUTHORIZATION=f'Bearer {issue_access_token(self.user.id)}')
 
@@ -94,7 +94,7 @@ class PublicIdTests(TestCase):
     def test_profile_shows_a_six_digit_code_that_maps_back_to_the_user(self):
         from accounts.public_id import decode
 
-        user = User.objects.create(device_id='public-id-device', is_guest=True)
+        user = User.objects.create(phone='09000000054')
         client = APIClient()
         client.credentials(HTTP_AUTHORIZATION=f'Bearer {issue_access_token(user.id)}')
         code = client.get('/api/user/profile').json()['publicId']