feat: event infrastructure — payload, transport, NATS adapter

- EventPublisher now takes &DomainEvent (11 call sites + 3 impls updated)
- EventEnvelope + EventConsumer port in domain
- event-payload: serializable DomainEvent mirror with subject routing
- event-transport: generic Transport/MessageSource traits, publisher/consumer adapters
- adapters-nats: JetStream publish + durable pull consumer

crates/worker/src/main.rs

@@ -55,7 +55,7 @@ struct LogEventPublisher;
 impl domain::ports::EventPublisher for LogEventPublisher {
     async fn publish(
         &self,
-        event: domain::events::DomainEvent,
+        event: &domain::events::DomainEvent,
     ) -> Result<(), domain::errors::DomainError> {
         info!(event = ?event, "domain event");
         Ok(())