feat(wfe-core): add LogSink trait and wire lifecycle publisher into executor

LogSink trait for real-time step output streaming. Added to
StepExecutionContext as optional field (backward compatible).
Threaded through WorkflowExecutor and WorkflowHostBuilder.

Wired LifecyclePublisher.publish() into executor at 5 points:
StepStarted, StepCompleted, Error, Completed, Terminated.
Also added lifecycle events to host start/suspend/resume/terminate.

wfe-core/src/primitives/mod.rs

@@ -45,6 +45,7 @@ mod test_helpers {
             workflow,
             cancellation_token: CancellationToken::new(),
             host_context: None,
+                log_sink: None,
         }
     }
 

wfe-core/src/primitives/sub_workflow.rs

@@ -212,6 +212,7 @@ mod tests {
             workflow,
             cancellation_token: tokio_util::sync::CancellationToken::new(),
             host_context: Some(host),
+            log_sink: None,
         }
     }