Bazaar: subscriptions (10343/10344), dynamic price (discount codes on Bazaar), auto-renewal sync

- Purchase with paymentMethod=bazaar now works for subscription plans with a bazaar_sku (not only packs);
  response carries bazaarProductType. Migration subscription.0014 puts 10343/10344 on the 90/180-day plans.
- Verify asks Bazaar for the right product type (from the order) and stores validUntil (payment.0012).
- POST /api/payment/bazaar/orders/{id}/start: SKU, type, and an HS256 dynamic-price JWT when a discount
  code lowered the price (BAZAAR_DYNAMIC_PRICE_KEY); discount on Bazaar orders allowed only with that key
  and only before start.
- Auto-renewal: sync_bazaar_renewals re-asks Bazaar when the paid period is near its end (status page and
  the paywall via has_subscription_access); each new period becomes a paid order.
- Default BAZAAR_PACKAGE_NAME = com.tadrisino.math.app; health shows bazaarDynamicPrice.
979 tests green. No real Bazaar purchase or renewal tested.

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

payment/serializers.py

@@ -25,6 +25,17 @@ class BazaarVerifyRequestSerializer(serializers.Serializer):
     purchaseToken = serializers.CharField()
 
 
+class BazaarStartResponseSerializer(serializers.Serializer):
+    orderId = serializers.CharField()
+    sku = serializers.CharField(help_text='productIdِ PurchaseRequestِ Poolakey.')
+    productType = serializers.ChoiceField(
+        choices=['inapp', 'subscription'],
+        help_text='inapp: purchaseProduct و بعد از تأییدِ سرور consume. subscription: subscribeProduct، بی‌consume.')
+    amount = serializers.IntegerField(help_text='مبلغِ سفارش (تومان)، پس از کدِ تخفیف.')
+    dynamicPriceToken = serializers.CharField(
+        allow_null=True, help_text='JWTِ «تخفیف پویا» برای PurchaseRequest.dynamicPriceToken؛ null یعنی قیمتِ پیشخان.')
+
+
 class BazaarVerifyResponseSerializer(serializers.Serializer):
     orderId = serializers.CharField()
     status = serializers.CharField()