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/application/src/catalog/commands/register_asset.rs

@@ -69,7 +69,7 @@ impl RegisterAssetHandler {
         };
 
         self.event_pub
-            .publish(DomainEvent::AssetIngested {
+            .publish(&DomainEvent::AssetIngested {
                 asset_id: asset.asset_id,
                 owner_user_id: asset.owner_user_id,
                 timestamp: DateTimeStamp::now(),

crates/application/src/catalog/commands/update_metadata.rs

@@ -43,7 +43,7 @@ impl UpdateMetadataHandler {
         self.metadata_repo.save(&metadata).await?;
 
         self.event_pub
-            .publish(DomainEvent::MetadataUpdated {
+            .publish(&DomainEvent::MetadataUpdated {
                 asset_id: cmd.asset_id,
                 updated_by: cmd.user_id,
                 timestamp: DateTimeStamp::now(),