Question packs removed at the root; all subscriptions 4 assistant questions a day; Bazaar is subscription-only

- subscription.0017/0018, payment.0013: pack plans deleted, QuestionCredit/HeartsPass models and Plan.kind /
  question_credits / hearts_days / Order.question_credits / hearts_days dropped. The only paid pack order was the
  company owner's test account (user 26).
- Assistant: no credit spending; quota is the daily cap only (free 2, every plan 4, gift subscription 4).
- Bazaar: verify_purchase is subscription-only (no inapp guess), start/purchase responses lose productType,
  verify refuses an order without a subscription. A paid order with no subscription now logs ERROR.
- Removed POST /api/payment/orders (internal; no caller). Its permission tests stay.
- Pack-based tests rewritten on subscriptions (refund, security, Bazaar token); pack-only test files deleted.
- docs: profit table for 4/day on both payment routes plus free users; handbook, operations, CLAUDE.md current.
949 tests green.

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

ai_tutor/serializers.py

@@ -35,7 +35,6 @@ class AskResponseSerializer(serializers.Serializer):
     answer = serializers.CharField()
     suggestedFollowUps = serializers.ListField(child=serializers.CharField())
     remainingQuota = serializers.IntegerField(help_text='سوال‌های رایگانِ باقیِ امروز.')
-    credits = serializers.IntegerField(required=False, help_text='اعتبارِ بسته‌های سوال (منقضی نمی‌شود).')
     diagram = serializers.DictField(required=False, allow_null=True)
     # تکه‌های درسیِ بازیابی‌شده از Qdrant که پاسخ بر پایه‌شون ساخته شده؛
     # خالی یعنی retrieval انجام نشده (نبودِ subject/lessonNumber یا خاموش‌بودنِ RAG).
@@ -72,4 +71,3 @@ class FeedbackResponseSerializer(serializers.Serializer):
 class QuotaResponseSerializer(serializers.Serializer):
     freeDaily = serializers.IntegerField(help_text='سوال‌های رایگانِ هر روز برای این کاربر.')
     remainingQuota = serializers.IntegerField(help_text='سوال‌های رایگانِ باقیِ امروز.')
-    credits = serializers.IntegerField(help_text='اعتبارِ بسته‌های سوال؛ منقضی نمی‌شود.')