feat: add daemon skeleton with lifecycle management

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/daemon/lifecycle.test.ts

@@ -0,0 +1,39 @@
+import { describe, it, expect, vi } from 'vitest';
+import { Lifecycle } from './lifecycle.js';
+
+describe('Lifecycle', () => {
+  it('registers and calls shutdown handlers in reverse order', async () => {
+    const lifecycle = new Lifecycle();
+    const calls: number[] = [];
+
+    lifecycle.onShutdown(async () => { calls.push(1); });
+    lifecycle.onShutdown(async () => { calls.push(2); });
+    lifecycle.onShutdown(async () => { calls.push(3); });
+
+    await lifecycle.shutdown();
+
+    expect(calls).toEqual([3, 2, 1]);
+  });
+
+  it('only shuts down once', async () => {
+    const lifecycle = new Lifecycle();
+    let count = 0;
+
+    lifecycle.onShutdown(async () => { count++; });
+
+    await lifecycle.shutdown();
+    await lifecycle.shutdown();
+
+    expect(count).toBe(1);
+  });
+
+  it('reports running state', async () => {
+    const lifecycle = new Lifecycle();
+
+    expect(lifecycle.isRunning).toBe(true);
+
+    await lifecycle.shutdown();
+
+    expect(lifecycle.isRunning).toBe(false);
+  });
+});