fix: Windows 桌面应用打包问题修复

- 删除通用 desktop target，重命名 platform targets 为简短形式 (desktop-mac/win/linux)
- 构建产物文件名统一为 nex-{os}-{arch}[.exe] 格式
- Windows 托盘图标使用 .ico 格式（运行时按平台选择）
- Windows 原生对话框使用 user32.MessageBoxW 替代 msg * 命令
- 更新 README.md 和 package-macos.sh 中的引用
- 添加单元测试覆盖 MessageBoxW 封装和图标选择逻辑
- 同步更新 desktop-app spec 规范文档

backend/cmd/desktop/main.go

@@ -12,7 +12,9 @@ import (
 	"path/filepath"
 	"runtime"
 	"strings"
+	"syscall"
 	"time"
+	"unsafe"
 
 	"github.com/gin-gonic/gin"
 	"github.com/getlantern/systray"
@@ -329,7 +331,13 @@ func setupStaticFiles(r *gin.Engine) {
 
 func setupSystray(port int) {
 	systray.Run(func() {
-		icon, err := embedfs.Assets.ReadFile("assets/icon.png")
+		var icon []byte
+		var err error
+		if runtime.GOOS == "windows" {
+			icon, err = embedfs.Assets.ReadFile("assets/icon.ico")
+		} else {
+			icon, err = embedfs.Assets.ReadFile("assets/icon.png")
+		}
 		if err != nil {
 			zapLogger.Error("无法加载托盘图标", zap.String("error", err.Error()))
 		}
@@ -446,7 +454,7 @@ func showError(title, message string) {
 		script := fmt.Sprintf(`display dialog "%s" buttons {"OK"} default button "OK" with title "%s"`, message, title)
 		exec.Command("osascript", "-e", script).Run()
 	case "windows":
-		exec.Command("msg", "*", message).Run()
+		messageBox(title, message, MB_ICONERROR)
 	case "linux":
 		exec.Command("zenity", "--error", fmt.Sprintf("--title=%s", title), fmt.Sprintf("--text=%s", message)).Run()
 	}
@@ -459,8 +467,29 @@ func showAbout() {
 		script := fmt.Sprintf(`display dialog "%s" buttons {"OK"} default button "OK" with title "关于 Nex Gateway"`, message)
 		exec.Command("osascript", "-e", script).Run()
 	case "windows":
-		exec.Command("msg", "*", message).Run()
+		messageBox("关于 Nex Gateway", message, MB_ICONINFORMATION)
 	case "linux":
 		exec.Command("zenity", "--info", "--title=关于 Nex Gateway", fmt.Sprintf("--text=%s", message)).Run()
 	}
 }
+
+const (
+	MB_ICONERROR      = 0x10
+	MB_ICONINFORMATION = 0x40
+)
+
+var (
+	user32          = syscall.NewLazyDLL("user32.dll")
+	procMessageBoxW = user32.NewProc("MessageBoxW")
+)
+
+func messageBox(title, message string, flags uint) {
+	titlePtr, _ := syscall.UTF16PtrFromString(title)
+	messagePtr, _ := syscall.UTF16PtrFromString(message)
+	procMessageBoxW.Call(
+		0,
+		uintptr(unsafe.Pointer(messagePtr)),
+		uintptr(unsafe.Pointer(titlePtr)),
+		uintptr(flags),
+	)
+}