refactor: code smell fixes — tests, events, naming

- Tests for ExecutePipelineHandler (happy path, fallback, disabled skip, failure retry, not found)
- Tests for ProcessNextJobHandler (empty queue, process, drain multiple)
- DerivativeGenerated domain event + event-payload mapping + event_store aggregate
- Renamed event-payload → adapters-event-payload, event-transport → adapters-event-transport

crates/adapters/event-transport/src/lib.rs

@@ -1,13 +1,13 @@
 pub mod composite;
 pub use composite::CompositeEventPublisher;
 
+use adapters_event_payload::EventPayload;
 use async_trait::async_trait;
 use domain::{
     errors::DomainError,
     events::{DomainEvent, EventEnvelope},
     ports::{EventConsumer, EventPublisher},
 };
-use event_payload::EventPayload;
 use futures::stream::BoxStream;
 
 #[async_trait]

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

@@ -55,7 +55,7 @@ async fn published_bytes_are_valid_json() {
     adapter.publish(&event).await.unwrap();
 
     let recorded = messages.lock().unwrap();
-    let payload: event_payload::EventPayload =
+    let payload: adapters_event_payload::EventPayload =
         serde_json::from_slice(&recorded[0].1).expect("should be valid JSON");
     assert_eq!(payload.subject(), "assets.ingested");
 }