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/checks/evidence.go

@@ -0,0 +1,31 @@
+// 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 checks
+
+import "encoding/json"
+
+// EvidenceJSON encodes evidence for transport to the agent API.
+func EvidenceJSON(ev map[string]any) json.RawMessage {
+	if len(ev) == 0 {
+		return json.RawMessage(`{}`)
+	}
+
+	b, err := json.Marshal(ev)
+	if err != nil {
+		return json.RawMessage(`{}`)
+	}
+
+	return json.RawMessage(b)
+}