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_freebsd.go

@@ -0,0 +1,97 @@
+// 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
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"os/exec"
+	"strings"
+	"text/template"
+)
+
+const (
+	rcScriptPath = "/usr/local/etc/rc.d/probo_agent"
+)
+
+// FreeBSD rc.d script template.
+const rcScriptTmpl = `#!/bin/sh
+#
+# PROVIDE: probo_agent
+# REQUIRE: NETWORKING
+# KEYWORD: shutdown
+
+. /etc/rc.subr
+
+name=probo_agent
+rcvar=probo_agent_enable
+desc="Probo device posture agent"
+pidfile="/var/run/${name}.pid"
+procname="{{.ExePath}}"
+command=/usr/sbin/daemon
+command_args="-r -P ${pidfile} -- \"{{.ExePath}}\" run --dir \"{{.Dir}}\""
+
+load_rc_config $name
+: ${probo_agent_enable:=YES}
+
+run_rc_command "$1"
+`
+
+func Install(cfg Config) error {
+	if cfg.ExePath == "" {
+		return errors.New("executable path is required")
+	}
+
+	if cfg.Dir == "" {
+		return errors.New("state directory is required")
+	}
+
+	rcTmpl, err := template.New("rc").Parse(rcScriptTmpl)
+	if err != nil {
+		return fmt.Errorf("cannot parse rc.d template: %w", err)
+	}
+
+	sf, err := os.OpenFile(rcScriptPath, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0o755)
+	if err != nil {
+		return fmt.Errorf("cannot write rc.d script (need root?): %w", err)
+	}
+
+	defer func() { _ = sf.Close() }()
+	if err := rcTmpl.Execute(sf, cfg); err != nil {
+		return fmt.Errorf("cannot render rc.d script: %w", err)
+	}
+
+	if out, err := exec.Command("service", "probo_agent", "enable").CombinedOutput(); err != nil {
+		return fmt.Errorf("cannot run service probo_agent enable: %w: %s", err, strings.TrimSpace(string(out)))
+	}
+
+	if out, err := exec.Command("service", "probo_agent", "start").CombinedOutput(); err != nil {
+		return fmt.Errorf("cannot run service probo_agent start: %w: %s", err, strings.TrimSpace(string(out)))
+	}
+
+	return nil
+}
+
+func Uninstall(cfg Config) error {
+	_ = exec.Command("service", "probo_agent", "stop").Run()
+	_ = exec.Command("service", "probo_agent", "disable").Run()
+
+	if err := os.Remove(rcScriptPath); err != nil && !errors.Is(err, os.ErrNotExist) {
+		return fmt.Errorf("cannot remove rc.d script: %w", err)
+	}
+
+	return nil
+}