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/bootstrap/src/log_event_publisher.rs

@@ -5,7 +5,7 @@ pub struct LogEventPublisher;
 
 #[async_trait]
 impl EventPublisher for LogEventPublisher {
-    async fn publish(&self, event: DomainEvent) -> Result<(), DomainError> {
+    async fn publish(&self, event: &DomainEvent) -> Result<(), DomainError> {
         tracing::info!(?event, "domain event published");
         Ok(())
     }