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>

js/test/machineId.test.ts

@@ -0,0 +1,44 @@
+import { mkdtempSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { afterEach, describe, expect, it, vi } from "vitest";
+import * as machineId from "../src/machineId.js";
+
+function tempInstallIdPath(): string {
+  const dir = mkdtempSync(join(tmpdir(), "origin-client-test-"));
+  return join(dir, "install-id");
+}
+
+describe("resolveMachineId", () => {
+  afterEach(() => {
+    machineId.machineIdDetector.current = machineId.detectOsMachineId;
+  });
+
+  it("prefers an explicit override", () => {
+    machineId.machineIdDetector.current = () => "os-machine-id";
+    expect(machineId.resolveMachineId("explicit-id", tempInstallIdPath())).toBe("explicit-id");
+  });
+
+  it("uses the OS machine id when available", () => {
+    machineId.machineIdDetector.current = () => "os-machine-id";
+    expect(machineId.resolveMachineId(undefined, tempInstallIdPath())).toBe("os-machine-id");
+  });
+
+  it("falls back to a generated id and persists it across calls", () => {
+    machineId.machineIdDetector.current = () => undefined;
+    const path = tempInstallIdPath();
+
+    const first = machineId.resolveMachineId(undefined, path);
+    expect(first.length).toBeGreaterThan(0);
+
+    const second = machineId.resolveMachineId(undefined, path);
+    expect(second).toBe(first);
+  });
+
+  it("logs a warning when the OS id is unavailable", () => {
+    machineId.machineIdDetector.current = () => undefined;
+    const warn = vi.fn();
+    machineId.resolveMachineId(undefined, tempInstallIdPath(), { warn });
+    expect(warn).toHaveBeenCalled();
+  });
+});