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/nats/Cargo.toml

@@ -5,7 +5,7 @@ edition = "2024"
 
 [dependencies]
 domain          = { workspace = true }
-event-transport = { workspace = true }
+adapters-event-transport = { workspace = true }
 async-nats      = { workspace = true }
 async-trait     = { workspace = true }
 futures         = { workspace = true }

crates/adapters/nats/src/lib.rs

@@ -1,7 +1,7 @@
+use adapters_event_transport::{MessageSource, RawMessage, Transport};
 use async_nats::jetstream::{self, AckKind, stream::Config as StreamConfig};
 use async_trait::async_trait;
 use domain::errors::DomainError;
-use event_transport::{MessageSource, RawMessage, Transport};
 use futures::stream::BoxStream;
 use std::sync::Arc;