Add message:received and message:sent events to the internal hook system,
enabling HOOK.md-based hooks to subscribe to message lifecycle events.
Changes:
- Add "message" to InternalHookEventType union
- Fire message:received internal hook in dispatch-from-config alongside
existing plugin hook (hoisted shared variables for both hook systems)
- Add onDelivered callback to ReplyDispatcherOptions for post-delivery hooks
- Fire message:sent internal hook + plugin hook after successful delivery
- Wire the existing (but previously unused) plugin message_sent hook
- Update docs: move message events from Future to documented event types
- Add tests for message:received and message:sent event handling
