feat(api): enable graceful shutdown hooks

Add NestJS shutdown hooks for proper SIGTERM handling, ensuring
database connections and in-flight requests are drained cleanly.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/api/src/main.ts

@@ -103,6 +103,9 @@ async function bootstrap() {
   // ── Trust Proxy (for rate limiting behind reverse proxy) ──
   expressApp.set('trust proxy', 1);
 
+  // ── Graceful Shutdown ──
+  app.enableShutdownHooks();
+
   const port = process.env['PORT'] ?? 3001;
   await app.listen(port);
   logger.log(`API running on http://localhost:${port}`, 'Bootstrap');