feat(workflows): TaskExecutorWorkflow stub + wire worker — T19/T20

activities.py — persist_task_instance (new):
  Idempotent INSERT ... ON CONFLICT (id) DO NOTHING on task_instances.
  task_id passed in from workflow (derived from workflow_id via uuid5).
  Registered on task-execution-tq.

workflows.py — TaskExecutorWorkflow (T19):
  Derives stable task_id = uuid5(NAMESPACE_URL, workflow_id).
  Calls persist_task_instance → status=done, returns immediately.
  Real execution logic to replace stub in a later workstream.

worker.py — T20:
  Registers persist_task_instance on task-execution-tq Worker.
  Both queues fully wired: orchestrator-tq and task-execution-tq.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/activity_core/worker.py

@@ -27,6 +27,7 @@ from activity_core.activities import (
     init_session_factory,
     load_activity_definition,
     log_run,
+    persist_task_instance,
     resolve_context,
 )
 from activity_core.workflows import RunActivityWorkflow, TaskExecutorWorkflow
@@ -57,7 +58,7 @@ async def run() -> None:
         client,
         task_queue=TASK_EXECUTION_TASK_QUEUE,
         workflows=[TaskExecutorWorkflow],
-        activities=[],
+        activities=[persist_task_instance],
     )
 
     async with orchestrator_worker, task_worker: