Install macOS helper from PKG for XPC enroll

Browser enrollment used osascript on every elevate. Ship a signed
privileged helper installed at PKG time so probo:// can enroll over
XPC with no second admin prompt. Add make install/uninstall/clean for
local PKG test loops, and show alerts only on failure.

Mirror the Go lint path for the macOS SPM package: Make
targets, root configs, and a Linux CI job. Keep checks
syntax-only so they do not need a macOS SDK. Format the
existing sources so the new gates start clean.

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

pkg/deviceagent/elevate/elevate_darwin_test.go

@@ -0,0 +1,48 @@
+// 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
+
+package elevate
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestRunElevatedInstallRequiresPrivilegedHelper(t *testing.T) {
+	t.Parallel()
+
+	err := RunElevatedInstall(
+		"/usr/local/bin/probo-agent",
+		"https://example.com",
+		"token",
+		"/var/lib/probo-agent",
+	)
+	require.ErrorIs(t, err, ErrPrivilegedHelperRequired)
+}
+
+func TestRunElevatedUninstallRequiresPrivilegedHelper(t *testing.T) {
+	t.Parallel()
+
+	err := RunElevatedUninstall("/usr/local/bin/probo-agent", "/var/lib/probo-agent")
+	require.ErrorIs(t, err, ErrPrivilegedHelperRequired)
+}