fix(server): register onClose hook before app.listen

Fastify forbids addHook after the instance is listening, so the
sweep-timer cleanup hook from 1.5.0 threw on every `serve` startup
and crashed the daemon. Register the hook first, then start
listening, and assign the timer through a ref.

node/src/server.ts

@@ -156,10 +156,11 @@ export async function startServer(
 ): Promise<{ app: FastifyInstance; store: MailboxStore; sweepTimer: NodeJS.Timeout | null }> {
   const store = new MailboxStore(cfg.dbPath);
   const app = await buildServer(cfg, store);
-  await app.listen({ host: cfg.bind, port: cfg.port });
+  const timerRef: { current: NodeJS.Timeout | null } = { current: null };
-  const sweepTimer = startSweep(store, cfg, app.log);
   app.addHook("onClose", async () => {
-    if (sweepTimer) clearInterval(sweepTimer);
+    if (timerRef.current) clearInterval(timerRef.current);
   });
-  return { app, store, sweepTimer };
+  await app.listen({ host: cfg.bind, port: cfg.port });
+  timerRef.current = startSweep(store, cfg, app.log);
+  return { app, store, sweepTimer: timerRef.current };
 }