Define mandate-delegation limits for coordinator-to-sub-agent handoff

## Description

No current item constrains what a coordinator/orchestrator agent is allowed to delegate to its sub-agents.

## Source

Krav 11 "Mandatoverdragelse og delegering": a coordinator can never delegate actions beyond its own mandate — e.g. a Class 2 coordinator cannot instruct a sub-agent to perform a Class 3 action.

## Business Goal

Without this rule, the classification and mandate limits defined elsewhere in this epic can be silently bypassed by routing a high-consequence action through a sub-agent.

## Acceptance Criteria

- Documented rule: a coordinator's own classification/mandate sets the absolute ceiling for anything it delegates.
- System documentation template (referenced from #75 / multi-agent registry entries) requires an explicit description of delegation boundaries.
- Cross-referenced from the approval-gate and kill-switch issues for multi-agent systems.

## Dependencies

Depends on the classification-scheme issue. Coordinates with the approval-gate and kill-switch issues.