fix: 修复所有 golangci-lint 错误

- goimports: 修复 3 个文件的导入顺序
- ineffassign: 移除无效的变量初始化
- staticcheck SA9003: 修复空分支问题

server/global/gateway/gateway.go

@@ -1,15 +1,15 @@
 package gateway
 
 import (
+	"next-terminal/server/common/term"
+	"next-terminal/server/utils"
+
 	"errors"
 	"fmt"
 	"net"
-	"next-terminal/server/common/term"
 	"os"
 	"sync"
 
-	"next-terminal/server/utils"
-
 	"golang.org/x/crypto/ssh"
 )