#791 Pause is advisory: engine keeps executing tasks of a paused workflow run

POST /workflows/<id>/pause (api/blueprints/v1/workflows.py:~3613) only sets workflow_run.status='paused'. No check in the worker claim/dispatch path consults that status, so already-queued jumper tasks keep being claimed and executed. Fix: engine-side check before task execution; if run paused, requeue with delay (do not consume a retry). Resume re-notifies. Demo-gated.