GTM API / Stop and delete mass-action

STOP a bulk run. This is the cancel path and it works at any status: pending and queued items are swept to cancelled, running items finish their current step and stop at the boundary, an auto-scrape feeding a standing run stops being able to append, and the run is soft-deleted. The cascade block reports how many were cancelled and how many were still in flight. Items stay queryable; there is no undo through MCP, and a plan cannot be edited, so restarting means a fresh preview and create. Contract: - MCP tool delete_mass_action, registry package mcp.orchestration/mass_actions, mount orchestration.mass_actions. - Operation delete, response envelope delete_cascade. - Flags: dangerous: the MCP layer gates it behind a preview/commit token, and the effect cannot be undone through this API.