Stop crashing the server on unhandled promise rejections

A single missed .catch() anywhere in the notification code (email/WhatsApp
sending) previously took down the whole process via process.exit(1). Log
the error instead and keep running.

backend/src/index.js

@@ -1265,11 +1265,12 @@ app.listen(PORT, () => {
   }
 });
 
-// Handle unhandled promise rejections
+// Log unhandled promise rejections without killing the server, since a single
+// missed .catch() on fire-and-forget notification code (email/WhatsApp sends)
+// would otherwise take the whole app down.
 process.on('unhandledRejection', (err) => {
-  console.log('UNHANDLED REJECTION! Shutting down...');
-  console.log(err.name, err.message);
-  process.exit(1);
+  console.error('UNHANDLED REJECTION!', err?.name, err?.message);
+  console.error(err?.stack || err);
 });
 
 module.exports = { app, prisma };