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/browser.go

@@ -0,0 +1,64 @@
+// 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 darwin || windows
+
+package tray
+
+import (
+	"fmt"
+	"net/url"
+	"os/exec"
+	"runtime"
+	"strings"
+)
+
+func openBrowser(rawURL string) error {
+	if err := validateBrowserURL(rawURL); err != nil {
+		return fmt.Errorf("cannot open browser URL: %w", err)
+	}
+
+	switch runtime.GOOS {
+	case "darwin":
+		return exec.Command("open", rawURL).Start()
+	case "windows":
+		return exec.Command(
+			"rundll32",
+			"url.dll,FileProtocolHandler",
+			rawURL,
+		).Start()
+	default:
+		return fmt.Errorf("unsupported platform %q", runtime.GOOS)
+	}
+}
+
+func validateBrowserURL(rawURL string) error {
+	parsed, err := url.Parse(rawURL)
+	if err != nil {
+		return fmt.Errorf("cannot parse URL: %w", err)
+	}
+
+	scheme := strings.ToLower(parsed.Scheme)
+	if scheme != "http" && scheme != "https" {
+		return fmt.Errorf("unsupported URL scheme %q", parsed.Scheme)
+	}
+
+	return nil
+}