Improve probo-agent tray icon and enrollment menu

Replace the placeholder orange-circle tray icon with the monochrome
Probo logo used in auditor-mode. On macOS, show the icon only (no
menu bar title); keep the title on Windows.

Restructure the context menu: status rows with colored indicators,
an Enroll via… submenu for region selection, and a clearer About
label. Surface enrollment errors in native dialogs instead of stderr.

Fix self-hosted enrollment on macOS by reading the hostname from
osascript's returned value; the default dialog output order broke
URL parsing and silently skipped opening the browser.

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

pkg/deviceagent/tray/tray_title_darwin.go

@@ -0,0 +1,29 @@
+// 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 && cgo
+
+package tray
+
+import "fyne.io/systray"
+
+func setTrayTitle() {
+	systray.SetTitle("")
+}