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>

subscription/views.py

@@ -112,8 +112,9 @@ class PurchaseView(APIView):
         plan = get_object_or_404(Plan, pk=v['planId'])
         idempotency_key = request.headers.get('Idempotency-Key')
 
-        # Three-phase flow so create_order (which may call an external payment
-        # gateway) never runs inside a DB transaction/lock: phase 1 creates/updates
+        # Three-phase flow so create_order never runs inside a DB transaction/lock.
+        # (create_order itself no longer calls Zarinpal — PaymentRedirectView
+        # does, on first visit — so this split is now defensive.) Phase 1 creates/updates
         # the pending Subscription, phase 2 calls create_order and restores the
         # prior state on failure, phase 3 attaches order_id atomically.
         existing_order = None