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/traits/mod.rs

@@ -1,5 +1,6 @@
 pub mod lifecycle;
 pub mod lock;
+pub mod log_sink;
 pub mod middleware;
 pub mod persistence;
 pub mod queue;
@@ -9,6 +10,7 @@ pub mod step;
 
 pub use lifecycle::LifecyclePublisher;
 pub use lock::DistributedLockProvider;
+pub use log_sink::{LogChunk, LogSink, LogStreamType};
 pub use middleware::{StepMiddleware, WorkflowMiddleware};
 pub use persistence::{
     EventRepository, PersistenceProvider, ScheduledCommandRepository, SubscriptionRepository,