Feature 1. work_item.created no longer starts the pipeline (soft QG-0 log only);
the issue stays in the backlog until moved to In Progress. The pipeline-start body
is extracted into start_pipeline(); a new issue updated handler routes a state
change to In Progress -> handle_status_start, which is idempotent: an existing task
for the plane_id is NOT re-created or restarted (protects handle_comment, which also
flips issues to In Progress). Real Plane payload: event=issue, action=updated,
data.state.id. Existing m6/plane_webhook/dedup tests updated to drive the new
trigger; new test_status_trigger.py covers created-no-op / start / idempotent.
