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>

cmd/probo-agent/installer/macos/enroll-ui/HelperTool/main.swift

@@ -0,0 +1,13 @@
+import Foundation
+import ProboAgentShared
+import os
+
+private let log = Logger(subsystem: "com.probo.agent.helper", category: "main")
+
+let helper = Helper()
+let listener = NSXPCListener(machServiceName: ProboAgentHelperConstants.machServiceName)
+listener.delegate = helper
+listener.resume()
+log.info("listening on \(ProboAgentHelperConstants.machServiceName, privacy: .public)")
+
+RunLoop.main.run()