- Add MessageResponseMode and messageResponseMode runtime config to core agent heartbeat types and exports
- Extend MessageStore with an onMessageToAgent hook plus runtime hook updates for agent-directed messages
- Wire HeartbeatMonitor to wake agents on incoming messages when messageResponseMode is immediate and state is eligible
- Update AgentDetailView with a Message Response Mode setting, validation, and runtimeConfig persistence
- Expand core and engine tests to cover hook behavior, wake-on-message triggering, and start/stop hook lifecycle