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/hostinfo_test.go

@@ -0,0 +1,57 @@
+package originclient
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestParseCgroupContainerID(t *testing.T) {
+	tests := []struct {
+		name string
+		data string
+		want string
+	}{
+		{
+			name: "cgroup v1 docker path",
+			data: "12:memory:/docker/9f8b7c6d5e4f3a2b1c0d9e8f7a6b5c4d3e2f1a0b9c8d7e6f5a4b3c2d1e0f9a8b\n",
+			want: "9f8b7c6d5e4f3a2b1c0d9e8f7a6b5c4d3e2f1a0b9c8d7e6f5a4b3c2d1e0f9a8b",
+		},
+		{
+			name: "cgroup v2 systemd scope",
+			data: "0::/system.slice/docker-9f8b7c6d5e4f3a2b1c0d9e8f7a6b5c4d3e2f1a0b9c8d7e6f5a4b3c2d1e0f9a8b.scope\n",
+			want: "9f8b7c6d5e4f3a2b1c0d9e8f7a6b5c4d3e2f1a0b9c8d7e6f5a4b3c2d1e0f9a8b",
+		},
+		{
+			name: "non-container host",
+			data: "0::/user.slice/user-1000.slice/session-2.scope\n",
+			want: "",
+		},
+		{
+			name: "empty",
+			data: "",
+			want: "",
+		},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			assert.Equal(t, tc.want, parseCgroupContainerID([]byte(tc.data)))
+		})
+	}
+}
+
+func TestIsContainerIDLike(t *testing.T) {
+	assert.True(t, isContainerIDLike("9f8b7c6d5e4f"))
+	assert.False(t, isContainerIDLike("short"))
+	assert.False(t, isContainerIDLike("session-2"))
+	assert.False(t, isContainerIDLike(""))
+}
+
+func TestOrchestrator_Kubernetes(t *testing.T) {
+	t.Setenv("KUBERNETES_SERVICE_HOST", "10.0.0.1")
+	assert.Equal(t, "kubernetes", Orchestrator())
+}
+
+func TestHostname_NotEmpty(t *testing.T) {
+	assert.NotEmpty(t, Hostname())
+}