Subscriptions only: Bazaar panel prices (598/898/1398k), assistant quota 5/3/3 from a cost calculation, packs off sale

- subscription.0016: prices equal to the Bazaar panel (senior), ai_daily_quota 5/3/3, card features; packs on_sale=False
  (one paid pack order, user 26, keeps its credits; pack paths stay for that order and for admin).
- Quota math in docs/ai-cost-and-guardrails.md: ~77% of a Bazaar sale reaches us; worst case (full quota every day)
  the assistant costs 23/27/35% of it.
- Assistant quota message points to the subscription, not packs.
982 tests green.

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

ai_tutor/tests_quota.py

@@ -30,7 +30,7 @@ class DailyQuotaTests(TestCase):
         self.assertEqual([self.ask().status_code for _ in range(2)], [200, 200])
         blocked = self.ask()
         self.assertEqual(blocked.status_code, 429)
-        self.assertIn('بسته', blocked.json()['detail'])
+        self.assertIn('اشتراک', blocked.json()['detail'])  # بسته از subscription.0016 فروخته نمی‌شود
 
     def test_remaining_quota_follows_the_users_own_limit(self):
         self.assertEqual(self.ask().json()['remainingQuota'], 1)