Add device agent library

Provide enrollment, elevated install, posture checks, keystore, and
system-tray helpers shared by the probo-agent binary.

Signed-off-by: Ludovic Vielle <ludovic@probo.com>

pkg/deviceagent/tray/messagebox_windows.go

@@ -0,0 +1,58 @@
+// Copyright (c) 2026 Probo Inc <hello@probo.com>.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+//go:build windows
+
+package tray
+
+import (
+	"unsafe"
+
+	"golang.org/x/sys/windows"
+)
+
+const (
+	mbOK              = 0x00000000
+	mbIconInformation = 0x00000040
+)
+
+var (
+	modUser32       = windows.NewLazySystemDLL("user32.dll")
+	procMessageBoxW = modUser32.NewProc("MessageBoxW")
+)
+
+func nativeMessageBox(title, message string, flags uint32) {
+	titleUTF16, err := windows.UTF16PtrFromString(title)
+	if err != nil {
+		return
+	}
+
+	messageUTF16, err := windows.UTF16PtrFromString(message)
+	if err != nil {
+		return
+	}
+
+	_, _, _ = procMessageBoxW.Call(
+		0,
+		uintptr(unsafe.Pointer(messageUTF16)),
+		uintptr(unsafe.Pointer(titleUTF16)),
+		uintptr(flags),
+	)
+}