Add probo-agent binary, installer, and CI

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

cmd/probo-agent/installer/macos/scripts/preinstall

@@ -0,0 +1,9 @@
+#!/bin/bash
+#
+# probo-agent macOS PKG preinstall script.
+#
+# Enrollment is handled by the menu bar helper after installation.
+# MDM may still pre-stage /tmp/probo-agent.conf for unattended
+# enrollment in postinstall.
+
+exit 0