feat: integrate Stripe payment with bugfixes and active timeout cancellation

- Add Stripe payment provider with Checkout Session flow
- Payment provider abstraction layer (EasyPay + Stripe unified interface)
- Stripe webhook with proper raw body handling and signature verification
- Frontend: Stripe button with URL validation, anti-duplicate click, noopener
- Active timeout cancellation: query platform before expiring, recover paid orders
- Singleton Stripe client, idempotency keys, Math.round for amounts
- Handle async_payment events, return null for unknown webhook events
- Set Checkout Session expires_at aligned with order timeout
- Add cancelPayment to provider interface (Stripe: sessions.expire, EasyPay: no-op)
- Enable stripe in frontend payment type list

docker-compose.prod.yml

@@ -3,7 +3,7 @@ services:
     image: sub2apipay:latest
     container_name: sub2apipay
     ports:
-      - "8087:3000"
+      - '8087:3000'
     env_file: .env
     networks:
       - sub2api-network