feat(jobs): pg-boss singleton client

Per-name ensureQueue promise dedup so concurrent enqueue+subscribe
on the same queue do not race createQueue (Postgres deadlock).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/jobs/queue.test.js

@@ -0,0 +1,21 @@
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import { resetDb } from '../helpers/db.js';
+import { migrateUp } from '../../lib/db/migrate.js';
+import { stopBoss } from '../helpers/boss.js';
+import * as queue from '../../lib/jobs/queue.js';
+
+beforeEach(async () => { await resetDb(); await migrateUp(); });
+afterEach(async () => { await stopBoss(); });
+
+describe('jobs/queue', () => {
+  it('starts, enqueues, and a worker receives the job', async () => {
+    await queue.start();
+    const received = new Promise(resolve => {
+      queue.subscribe('echo-q', async job => { resolve(job.data); });
+    });
+    const jobId = await queue.enqueue('echo-q', { hello: 'void' });
+    expect(jobId).toBeTruthy();
+    const data = await received;
+    expect(data).toEqual({ hello: 'void' });
+  });
+});