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

relaykit/reasonmap/reasonmap.go

@@ -0,0 +1,41 @@
+package reasonmap
+
+import (
+	"strings"
+
+	"github.com/QuantumNous/new-api/relaykit/types"
+)
+
+func ClaudeStopReasonToOpenAIFinishReason(stopReason string) string {
+	switch strings.ToLower(stopReason) {
+	case "stop_sequence":
+		return "stop"
+	case "end_turn":
+		return "stop"
+	case "max_tokens":
+		return "length"
+	case "tool_use":
+		return "tool_calls"
+	case "refusal":
+		return types.FinishReasonContentFilter
+	default:
+		return stopReason
+	}
+}
+
+func OpenAIFinishReasonToClaudeStopReason(finishReason string) string {
+	switch strings.ToLower(finishReason) {
+	case "stop":
+		return "end_turn"
+	case "stop_sequence":
+		return "stop_sequence"
+	case "length", "max_tokens":
+		return "max_tokens"
+	case types.FinishReasonContentFilter:
+		return "refusal"
+	case "tool_calls":
+		return "tool_use"
+	default:
+		return finishReason
+	}
+}