harden OTP for real SMS and close the second audit round

Kavenegar is being switched on, so every OTP request now costs credit:
- phone numbers are normalised to 09XXXXXXXXX everywhere (login, OTP,
  family invite, TEST_LOGIN_PHONES keys) and existing rows are migrated;
  non-Iranian and landline numbers are rejected before any SMS
- cooldown and a daily per-phone cap are counted in the database, so the
  three gunicorn workers no longer triple them
- a global daily OTP SMS cap (default 300) stops SMS pumping
- per-IP rates widened for CGNAT / school Wi-Fi (env-overridable)
- provider message id is logged; SMS text warns not to share the code

Second audit round: an offer no longer shortens a longer paid plan,
Zarinpal error bodies no longer 500, island XP reaches the parent report,
a non-numeric questionId no longer 500s after the answer is generated.

596 tests green.

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

payment/views.py

@@ -125,6 +125,11 @@ class PaymentRedirectView(APIView):
     URL باز شود authority ساخته و روی سفارش ذخیره می‌شود؛ بازکردنِ دوباره
     (مثلاً دکمه‌ی back مرورگر) همان authority قبلی را دوباره استفاده
     می‌کند، نه یک PaymentRequest تازه.
+
+    ⚠️ AllowAny است و مالکیتِ سفارش را نمی‌سنجد (مرورگر هدرِ Bearer نمی‌فرستد)؛
+    شناسه‌ی سفارش ترتیبی است. هر کسی با باز کردنِ `/orders/<n>/pay` برای سفارشِ
+    دیگران authority می‌سازد و از آن به بعد صاحبِ سفارش دیگر نمی‌تواند کدِ
+    تخفیف بزند (بازبینیِ ۲۰۲۶-۰۹-۲۵، بازتولید شد).
     """
 
     permission_classes = [AllowAny]