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

relay/constant/relay_mode_test.go

@@ -0,0 +1,22 @@
+package constant
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestPath2RelayMode(t *testing.T) {
+	tests := []struct {
+		path string
+		want int
+	}{
+		{path: "/v1/alpha/search", want: RelayModeAlphaSearch},
+		{path: "/v1/alpha/search?foo=1", want: RelayModeAlphaSearch},
+	}
+	for _, tt := range tests {
+		t.Run(tt.path, func(t *testing.T) {
+			assert.Equal(t, tt.want, Path2RelayMode(tt.path))
+		})
+	}
+}