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/Cargo.toml

@@ -1,11 +1,11 @@
 [package]
-name = "event-transport"
+name = "adapters-event-transport"
 version = "0.1.0"
 edition = "2024"
 
 [dependencies]
 domain        = { workspace = true }
-event-payload = { workspace = true }
+adapters-event-payload = { workspace = true }
 serde_json    = { workspace = true }
 async-trait   = { workspace = true }
 tracing       = { workspace = true }