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/hostinfo.go

@@ -0,0 +1,98 @@
+// 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 deviceagent
+
+import (
+	"context"
+	"crypto/sha256"
+	"encoding/hex"
+	"net"
+	"os"
+	"os/exec"
+	"strings"
+)
+
+type (
+	// HostInfo is the device identity reported by the agent.
+	HostInfo struct {
+		Hostname     string
+		Platform     string
+		OSVersion    string
+		HardwareUUID string
+		SerialNumber *string
+	}
+)
+
+// CollectHostInfo gathers host identity using best-effort probes.
+func CollectHostInfo() HostInfo {
+	info := HostInfo{
+		Platform: platformString(),
+	}
+
+	if h, err := os.Hostname(); err == nil {
+		info.Hostname = h
+	}
+
+	if info.Hostname == "" {
+		info.Hostname = "unknown-host"
+	}
+
+	info.OSVersion = collectOSVersion()
+	info.HardwareUUID = collectHardwareUUID()
+	if sn := collectSerialNumber(); sn != "" {
+		info.SerialNumber = &sn
+	}
+
+	return info
+}
+
+// hashFallbackUUID derives a stable fallback from hostname and MAC.
+func hashFallbackUUID() string {
+	hostname, _ := os.Hostname()
+	mac := firstStableMAC()
+	h := sha256.New()
+	h.Write([]byte(hostname))
+	h.Write([]byte{0})
+	h.Write([]byte(mac))
+	return hex.EncodeToString(h.Sum(nil))
+}
+
+func firstStableMAC() string {
+	ifaces, err := net.Interfaces()
+	if err != nil {
+		return ""
+	}
+
+	for _, ifc := range ifaces {
+		if ifc.Flags&net.FlagLoopback != 0 {
+			continue
+		}
+
+		if len(ifc.HardwareAddr) == 0 {
+			continue
+		}
+
+		return ifc.HardwareAddr.String()
+	}
+
+	return ""
+}
+
+// runQuiet runs a command and returns trimmed stdout.
+func runQuiet(ctx context.Context, name string, args ...string) (string, error) {
+	cmd := exec.CommandContext(ctx, name, args...)
+	out, err := cmd.Output()
+	return strings.TrimSpace(string(out)), err
+}