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/helpers/boss.js

@@ -0,0 +1,23 @@
+import * as queue from '../../lib/jobs/queue.js';
+import { pool } from '../../lib/db/pool.js';
+
+export async function stopBoss() {
+  try { await queue.stop(); } catch { /* ignore */ }
+  try { await pool.query('DROP SCHEMA IF EXISTS pgboss CASCADE'); } catch { /* ignore */ }
+}
+
+export async function waitForJob(id, { timeoutMs = 5_000 } = {}) {
+  const boss = queue.instance();
+  if (!boss) throw new Error('queue not started');
+  const start = Date.now();
+  while (Date.now() - start < timeoutMs) {
+    const j = await boss.getJobById(id);
+    if (!j) {
+      await new Promise(r => setTimeout(r, 50));
+      continue;
+    }
+    if (['completed','failed','cancelled','expired'].includes(j.state)) return j;
+    await new Promise(r => setTimeout(r, 50));
+  }
+  throw new Error(`job ${id} did not finish in ${timeoutMs} ms`);
+}