GTM API / Pause mass-action

Freeze dispatch: status becomes paused with paused_reason='manual'. Queued jobs roll back at pre-flight and in-flight items finish their current step, then stop at the boundary; vendor calls already on the wire are never aborted. Pass hold_till to arm auto-resume at that moment, omit it to wait for an explicit resume_mass_action. Idempotent: pausing a paused run refreshes it, and a manual pause replaces a limit_reached hold (its hold_till goes). Contract: - MCP tool pause_mass_action, registry package mcp.orchestration/mass_actions, mount orchestration.mass_actions. - Operation action, response envelope action. - Flags: none.