feat: add graceful shutdown and PM2 cross-worker messaging

Close all tenant DB pools on SIGTERM/SIGINT for clean restarts.
Support PM2 cluster invalidate-tenant-cache messages.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/api/src/index.ts

@@ -1,10 +1,11 @@
 import { app } from './app.js';
 import { env } from './config/env.js';
+import { tenantDb } from './config/database.js';
 import { startSatSyncJob } from './jobs/sat-sync.job.js';
 
 const PORT = parseInt(env.PORT, 10);
 
-app.listen(PORT, '0.0.0.0', () => {
+const server = app.listen(PORT, '0.0.0.0', () => {
   console.log(`API Server running on http://0.0.0.0:${PORT}`);
   console.log(`Environment: ${env.NODE_ENV}`);
 
@@ -13,3 +14,23 @@ app.listen(PORT, '0.0.0.0', () => {
     startSatSyncJob();
   }
 });
+
+// Graceful shutdown — close all tenant DB pools before exiting
+const gracefulShutdown = async (signal: string) => {
+  console.log(`${signal} received. Shutting down gracefully...`);
+  server.close(() => {
+    console.log('HTTP server closed');
+  });
+  await tenantDb.shutdown();
+  process.exit(0);
+};
+
+process.on('SIGTERM', () => gracefulShutdown('SIGTERM'));
+process.on('SIGINT', () => gracefulShutdown('SIGINT'));
+
+// PM2 cluster: cross-worker cache invalidation
+process.on('message', (msg: any) => {
+  if (msg?.type === 'invalidate-tenant-cache' && msg.tenantId) {
+    tenantDb.invalidatePool(msg.tenantId);
+  }
+});