Add probo-agent CLI and deviceagent library

Introduce the standalone device agent binary and shared library
for enrollment, posture checks, self-update, and OS service
integration. Include build targets, module deps, and release
workflow so the agent can ship independently of server changes.

Signed-off-by: Bryan Frimin <bryan@probo.com>

pkg/deviceagent/service/service.go

@@ -0,0 +1,33 @@
+// Copyright (c) 2025-2026 Probo Inc <hello@getprobo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+// Package service installs and uninstalls OS service units for probo-agent.
+package service
+
+// Config carries installation parameters shared across platforms.
+type Config struct {
+	// ExePath is the agent binary path.
+	ExePath string
+	// Dir is the agent state directory.
+	Dir string
+	// Label is the service identifier.
+	Label string
+}
+
+// Default service identifiers by platform.
+const (
+	DefaultLabel       = "com.getprobo.agent"
+	DefaultUnixName    = "probo-agent"
+	DefaultWindowsName = "ProboAgent"
+)