fix: 修复 macOS 桌面应用打包与元数据

将 macOS 桌面应用改为通用二进制并动态写入最低系统版本，避免 Intel Mac 无法启动。统一桌面应用名称与托盘展示，并补充测试确保相关行为稳定。

backend/cmd/desktop/dialog_linux.go

@@ -67,21 +67,19 @@ func showError(title, message string) {
 }
 
 func showAbout() {
-	message := "Nex Gateway\n\nAI Gateway - 统一的大模型 API 网关\n\nhttps://github.com/nex/gateway"
-
 	switch dialogTool {
 	case toolZenity:
 		exec.Command("zenity", "--info",
-			"--title=关于 Nex Gateway",
-			fmt.Sprintf("--text=%s", message)).Run()
+			fmt.Sprintf("--title=%s", appAboutTitle),
+			fmt.Sprintf("--text=%s", aboutMessage())).Run()
 	case toolKdialog:
-		exec.Command("kdialog", "--msgbox", message, "--title", "关于 Nex Gateway").Run()
+		exec.Command("kdialog", "--msgbox", aboutMessage(), "--title", appAboutTitle).Run()
 	case toolNotifySend:
-		exec.Command("notify-send", "关于 Nex Gateway", message).Run()
+		exec.Command("notify-send", appAboutTitle, aboutMessage()).Run()
 	case toolXmessage:
 		exec.Command("xmessage", "-center",
-			fmt.Sprintf("关于 Nex Gateway: %s", message)).Run()
+			fmt.Sprintf("%s: %s", appAboutTitle, aboutMessage())).Run()
 	default:
-		dialogLogger().Info("关于 Nex Gateway")
+		dialogLogger().Info(appAboutTitle)
 	}
 }