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_windows.go

@@ -0,0 +1,21 @@
+//go:build windows
+
+package originclient
+
+import "golang.org/x/sys/windows/registry"
+
+// machineID reads MachineGuid from the registry, which is generated at
+// Windows install time and stable across reboots.
+func machineID() (string, error) {
+	key, err := registry.OpenKey(registry.LOCAL_MACHINE, `SOFTWARE\Microsoft\Cryptography`, registry.QUERY_VALUE|registry.WOW64_64KEY)
+	if err != nil {
+		return "", err
+	}
+	defer key.Close()
+
+	value, _, err := key.GetStringValue("MachineGuid")
+	if err != nil {
+		return "", err
+	}
+	return value, nil
+}