feat: integrate CREEM web payment for credits purchase

Replace abandoned iOS App Store route with CREEM Merchant of Record
payment integration for web-based credits purchase.

Backend changes:
- Add CreemClient for CREEM API communication
- Add CreemService for checkout creation and webhook handling
- Add creem_transactions table for payment tracking
- Fix webhook payload parsing (id, order.id, customer.id structure)
- Integrate with existing points ledger system

Frontend changes:
- Display dynamic prices from CREEM API
- Support decimal price formatting (e.g., $1.00)
- Add checkout flow with redirect to CREEM hosted page

.env.example

@@ -5,6 +5,7 @@
 # 运行时配置
 ############
 ERYAO_RUNTIME__ENVIRONMENT=dev
+ERYAO_RUNTIME__DEBUG=true
 ERYAO_RUNTIME__LOG_LEVEL=INFO
 ERYAO_RUNTIME__SQL_LOG_QUERIES=false
 ERYAO_RUNTIME__TRUSTED_PROXY_IPS='["127.0.0.1", "172.18.0.1"]'
@@ -105,9 +106,21 @@ ERYAO_TEST__CODE=123456
 # Apple IAP 配置
 ############
 ERYAO_APPLE_IAP__BUNDLE_ID=com.meeyao.qianwen
-# Apple IAP 环境识别。auto 表示以后端验签后的 Apple transaction environment 为准。
-ERYAO_APPLE_IAP__ENVIRONMENT=auto
 # Server API 密钥（可选，用于主动查询交易状态）
 ERYAO_APPLE_IAP__SERVER_API_KEY_ID=
 ERYAO_APPLE_IAP__SERVER_API_PRIVATE_KEY=
 ERYAO_APPLE_IAP__SERVER_API_ISSUER_ID=
+# 沙盒测试账号（仅用于手动测试，不用于后端验证）
+ERYAO_APPLE_IAP__SANDBOX_TESTER_EMAIL=
+ERYAO_APPLE_IAP__SANDBOX_TESTER_PASSWORD=
+# Server Notifications V2 URL（在 App Store Connect 中配置）
+# 格式: https://<your-domain>/api/v1/payments/apple/notifications
+ERYAO_APPLE_IAP__SERVER_NOTIFICATIONS_URL=
+
+############
+# CREEM Payment 配置
+############
+ERYAO_CREEM__API_KEY=
+ERYAO_CREEM__WEBHOOK_SECRET=
+ERYAO_CREEM__BASE_URL=https://test-api.creem.io
+ERYAO_CREEM__SUCCESS_URL=https://yourdomain.com/store?payment=success