Add tray browser enrollment with region picker

The tray helper carried a ServerURL default that nothing read.
Unenrolled users can now open the console /enroll page from the
menu: US, EU, or self-hosted in production, or --server for dev.

Signed-off-by: Ludovic Vielle <ludovic@probo.com>
Co-authored-by: Cursor <cursoragent@cursor.com>

pkg/deviceagent/tray/prompt_hostname_windows.go

@@ -0,0 +1,56 @@
+// 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 (
+	"os/exec"
+	"strings"
+)
+
+func promptSelfHostedHostname() (string, bool) {
+	script := `
+Add-Type -AssemblyName Microsoft.VisualBasic
+[Microsoft.VisualBasic.Interaction]::InputBox(
+  'Enter your Probo hostname:',
+  'Probo Device Posture Agent',
+  ''
+)
+`
+	out, err := exec.Command(
+		"powershell",
+		"-NoProfile",
+		"-NonInteractive",
+		"-Command",
+		script,
+	).Output()
+	if err != nil {
+		return "", false
+	}
+
+	hostname := strings.TrimSpace(string(out))
+	if hostname == "" {
+		return "", false
+	}
+
+	return hostname, true
+}