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

model/locking.go

@@ -0,0 +1,25 @@
+package model
+
+import (
+	"github.com/QuantumNous/new-api/common"
+
+	"gorm.io/gorm"
+	"gorm.io/gorm/clause"
+)
+
+// lockForUpdate makes the next query emit SELECT ... FOR UPDATE so the matched
+// rows stay locked until the surrounding transaction ends.
+//
+// GORM v2 silently ignores the legacy `Set("gorm:query_option", "FOR UPDATE")`
+// from GORM v1, so that form does not lock anything. Always use this helper
+// instead.
+//
+// SQLite has no FOR UPDATE syntax (the clause would be a syntax error), so it
+// is skipped there; SQLite's single-writer model makes one of two conflicting
+// transactions fail instead of both committing.
+func lockForUpdate(tx *gorm.DB) *gorm.DB {
+	if common.UsingMainDatabase(common.DatabaseTypeSQLite) {
+		return tx
+	}
+	return tx.Clauses(clause.Locking{Strength: "UPDATE"})
+}