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/domain/src/common/events.rs

@@ -1,5 +1,12 @@
 use crate::common::value_objects::{DateTimeStamp, SystemId};
 
+pub struct EventEnvelope {
+    pub event: DomainEvent,
+    pub delivery_count: u64,
+    pub ack: Box<dyn Fn() + Send + Sync>,
+    pub nack: Box<dyn Fn() + Send + Sync>,
+}
+
 #[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
 pub enum DomainEvent {
     AssetIngested {

crates/domain/src/common/ports.rs

@@ -1,8 +1,13 @@
 use crate::common::errors::DomainError;
-use crate::common::events::DomainEvent;
+use crate::common::events::{DomainEvent, EventEnvelope};
 use async_trait::async_trait;
+use futures::stream::BoxStream;
 
 #[async_trait]
 pub trait EventPublisher: Send + Sync {
-    async fn publish(&self, event: DomainEvent) -> Result<(), DomainError>;
+    async fn publish(&self, event: &DomainEvent) -> Result<(), DomainError>;
+}
+
+pub trait EventConsumer: Send + Sync {
+    fn consume(&self) -> BoxStream<'_, Result<EventEnvelope, DomainError>>;
 }