Security review fixes: admin permissions, guest sessions, payment edge cases, assistant leaks

- Admin: refund/cancel/mark-resolved/Bazaar-link actions need change permission; question and
  curriculum import need add/delete; content browser needs view_question; guest device ids are
  shown to superusers only.
- Accounts: registering a guest's phone revokes the guest's earlier sessions; self-deletion keeps
  Redemption, UserOffer and the phone's OTP rows; the public demo guest cannot be deleted
  (DEMO_GUEST_DEVICE_IDS); display-name contact filter covers any separator and social handles.
- Payment: callback without Authority is 400; a second Bazaar purchase on a paid order is 409;
  orders snapshot credits/hearts/days at creation (payment.0011).
- Assistant: a broken diagram no longer makes a streamed answer free; a late off-topic marker
  refuses the answer (not stored, not cached); a disconnect saves the partial answer; only
  KNOWN_COLLECTIONS are searched.
- Infra: secret-key file is created atomically (workers no longer split keys); no default
  INTERNAL_SERVICE_KEY; Kavenegar key and Bazaar token kept out of error logs; Swagger/ReDoc
  pinned; schema throttled; docker compose bound to 127.0.0.1; non-ASCII digit ids are 400;
  ticket text capped at 5000.
- docs/security-before-production.md: remaining open items 24-31 and the guard tests.

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

progress/views.py

@@ -255,7 +255,10 @@ class SelectCharacterView(APIView):
     def post(self, request):
         serializer = SelectCharacterRequestSerializer(data=request.data)
         serializer.is_valid(raise_exception=True)
-        character = get_object_or_404(Character, pk=serializer.validated_data['characterId'])
+        character_id = serializer.validated_data['characterId']
+        if not (character_id.isascii() and character_id.isdigit()):
+            raise ValidationError({'characterId': 'شناسه‌ی کاراکتر باید عدد باشد.'})
+        character = get_object_or_404(Character, pk=int(character_id))
 
         stats, _ = UserStats.objects.get_or_create(user_id=request.user.id)
         if stats.xp < character.unlock_xp: