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/adapters/event-transport/src/tests.rs

@@ -0,0 +1,61 @@
+use crate::{EventPublisherAdapter, Transport};
+use async_trait::async_trait;
+use domain::{
+    errors::DomainError, events::DomainEvent, ports::EventPublisher, value_objects::SystemId,
+};
+use std::sync::{Arc, Mutex};
+
+struct RecordingTransport {
+    messages: Arc<Mutex<Vec<(String, Vec<u8>)>>>,
+}
+
+#[async_trait]
+impl Transport for RecordingTransport {
+    async fn publish_bytes(&self, subject: &str, bytes: &[u8]) -> Result<(), DomainError> {
+        self.messages
+            .lock()
+            .unwrap()
+            .push((subject.to_string(), bytes.to_vec()));
+        Ok(())
+    }
+}
+
+#[tokio::test]
+async fn adapter_publishes_with_correct_subject() {
+    let messages = Arc::new(Mutex::new(Vec::new()));
+    let adapter = EventPublisherAdapter::new(RecordingTransport {
+        messages: messages.clone(),
+    });
+
+    let event = DomainEvent::JobCompleted {
+        job_id: SystemId::new(),
+        timestamp: domain::value_objects::DateTimeStamp::now(),
+    };
+
+    adapter.publish(&event).await.unwrap();
+
+    let recorded = messages.lock().unwrap();
+    assert_eq!(recorded.len(), 1);
+    assert_eq!(recorded[0].0, "jobs.completed");
+}
+
+#[tokio::test]
+async fn published_bytes_are_valid_json() {
+    let messages = Arc::new(Mutex::new(Vec::new()));
+    let adapter = EventPublisherAdapter::new(RecordingTransport {
+        messages: messages.clone(),
+    });
+
+    let event = DomainEvent::AssetIngested {
+        asset_id: SystemId::new(),
+        owner_user_id: SystemId::new(),
+        timestamp: domain::value_objects::DateTimeStamp::now(),
+    };
+
+    adapter.publish(&event).await.unwrap();
+
+    let recorded = messages.lock().unwrap();
+    let payload: event_payload::EventPayload =
+        serde_json::from_slice(&recorded[0].1).expect("should be valid JSON");
+    assert_eq!(payload.subject(), "assets.ingested");
+}