feat(waffo): Waffo payment gateway integration with configurable methods

- Add Waffo payment SDK integration (waffo-go v1.3.1)
- Backend: webhook handler, pay endpoint, order lock race-condition fix
- Settings: full Waffo config (API keys, sandbox/prod, currency, pay methods)
- Frontend: Waffo payment buttons in topup page, admin settings panel
- i18n: Waffo-related translations for en/fr/ja/ru/vi/zh-TW

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

web/src/i18n/locales/en.json

@@ -3216,6 +3216,16 @@
     "默认测试模型": "Default Test Model",
     "默认用户消息": "Default User Message",
     "默认补全倍率": "Default completion ratio",
+    "提示：端点映射仅用于模型广场展示，不会影响模型真实调用。如需配置真实调用，请前往「渠道管理」。": "Notice: Endpoint mapping is for Model Marketplace display only and does not affect real model invocation. To configure real invocation, please go to Channel Management.",
+    "购买订阅获得模型额度/次数": "Purchase a subscription to get model quota/usage",
+    "生产环境 RSA 私钥 Base64 (PKCS#8 DER)": "Production RSA private key Base64 (PKCS#8 DER)",
+    "沙盒环境 RSA 私钥 Base64 (PKCS#8 DER)": "Sandbox RSA private key Base64 (PKCS#8 DER)",
+    "生产环境 Waffo 公钥 Base64 (X.509 DER)": "Production Waffo public key Base64 (X.509 DER)",
+    "沙盒环境 Waffo 公钥 Base64 (X.509 DER)": "Sandbox Waffo public key Base64 (X.509 DER)",
+    "支付方式类型": "Pay Method Type",
+    "支付方式名称": "Pay Method Name",
+    "获取充值配置失败": "Failed to get topup configuration",
+    "获取充值配置异常": "Topup configuration error",
     "分组相关设置": "Group Related Settings",
     "保存分组相关设置": "Save Group Related Settings",
     "此页面仅显示未设置价格或基础倍率的模型，设置后会自动从列表中移出": "This page only shows models without base pricing. After saving, configured models will be removed from this list automatically.",