feat: 算力引擎 Go 后端核心（new-api）

- 统一 OpenAI 兼容 /v1 中继 + 渠道/额度/令牌/流水
- 各领域包：relay 模型网关、model 数据层、controller 管理 API

setting/payment_waffo_pancake.go

@@ -0,0 +1,15 @@
+package setting
+
+// Waffo Pancake hosted checkout configuration. Gateway is enabled once
+// MerchantID + PrivateKey + ProductID are populated (no separate Enabled
+// flag, matching Stripe / Creem). StoreID + ProductID are operator-bound
+// via SaveWaffoPancakeConfig.
+var (
+	WaffoPancakeMerchantID string
+	WaffoPancakePrivateKey string
+	WaffoPancakeReturnURL  string
+	WaffoPancakeUnitPrice  float64 = 1.0
+	WaffoPancakeMinTopUp   int     = 1
+	WaffoPancakeStoreID    string
+	WaffoPancakeProductID  string
+)