feat: notify configured recipients when something is booked

config/packages/messenger.yaml

@@ -18,7 +18,13 @@ framework:
             messenger.bus.default: []
 
         routing:
-            Symfony\Component\Mailer\Messenger\SendEmailMessage: async
+            # Mail is deliberately NOT routed to async. Nothing starts a worker on the server --
+            # deploy.php only stops them -- so a queued SendEmailMessage would be written to
+            # messenger_messages and stay there, with no error anywhere and nobody notified.
+            # Sending happens in the request instead; BookingNotifier catches a transport
+            # failure so it can never fail the booking that triggered it. Route it back here
+            # once a `messenger:consume async` worker actually runs.
+            # Symfony\Component\Mailer\Messenger\SendEmailMessage: async
             Symfony\Component\Notifier\Message\ChatMessage: async
             Symfony\Component\Notifier\Message\SmsMessage: async