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>

discount/views.py

@@ -56,6 +56,9 @@ class GuestAwareDiscountThrottle(ScopedRateThrottle):
 
 
 def _is_usable(discount: DiscountCode) -> bool:
+    # ⚠️ هر Redemption شمرده می‌شود، حتی روی سفارشی که هرگز پرداخت نشد؛ پس
+    # سبدِ رهاشده سهمِ max_uses را برای همیشه می‌سوزاند و خودِ همان کاربر هم
+    # روی سفارشِ تازه‌اش دیگر نمی‌تواند کد بزند (بازبینیِ ۲۰۲۶-۰۹-۲۵، بازتولید شد).
     return bool(
         discount.redemptions.count() < discount.max_uses
         and (discount.expires_at is None or discount.expires_at >= timezone.now())