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>

subscription/tests_packs.py

@@ -32,7 +32,7 @@ def _client(user):
 class _Base(TestCase):
     def setUp(self):
         cache.clear()
-        self.user = User.objects.create(phone='09120005001', is_guest=False)
+        self.user = User.objects.create(phone='09120005001')
         self.client = _client(self.user)
         self.pack60 = Plan.objects.get(kind='pack', question_credits=60)