feat: initial Go/JS/Rust Origin check-in client SDKs

Standalone clients that resolve a machine unique ID (OS machine ID first,
falling back to a generated UUID persisted to disk), detect hostname/IP/
container/orchestrator, and register+re-ping origin.warky.dev's public
service-checkin endpoint on a daily interval. Ported from icy2's internal
origincheckin package but extended to the full check-in contract and made
dependency-light for external reuse.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

go/machineid_darwin.go

@@ -0,0 +1,29 @@
+//go:build darwin
+
+package originclient
+
+import (
+	"context"
+	"os/exec"
+	"regexp"
+	"time"
+)
+
+var ioregUUIDPattern = regexp.MustCompile(`"IOPlatformUUID" = "([0-9A-Fa-f-]+)"`)
+
+// machineID reads the hardware IOPlatformUUID via ioreg, which is stable
+// across reboots and unique per physical/virtual Mac.
+func machineID() (string, error) {
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+
+	out, err := exec.CommandContext(ctx, "ioreg", "-rd1", "-c", "IOPlatformExpertDevice").Output()
+	if err != nil {
+		return "", err
+	}
+	match := ioregUUIDPattern.FindSubmatch(out)
+	if match == nil {
+		return "", errMachineIDUnavailable
+	}
+	return string(match[1]), nil
+}