fix: pass sessionKey to deliverOutboundPayloads for message:sent hook dispatch

Several call sites of deliverOutboundPayloads() were not passing the
sessionKey parameter, causing the internal message:sent hook to never
fire (the guard `if (!sessionKeyForInternalHooks) return` in deliver.ts
silently skipped the triggerInternalHook call).

Fixed call sites:
- commands/agent/delivery.ts (agent loop replies — main fix)
- infra/heartbeat-runner.ts (heartbeat OK + alert delivery)
- infra/outbound/message.ts (message tool sends)
- cron/isolated-agent/delivery-dispatch.ts (cron job delivery)
- gateway/server-node-events.ts (node event forwarding)

The sessionKey parameter already existed in DeliverOutboundPayloadsCoreParams
and was used by deliver.ts to emit the message:sent internal hook event,
but was simply not being passed from most callers.

src/infra/outbound/message.ts

@@ -233,6 +233,7 @@ export async function sendMessage(params: MessageSendParams): Promise<MessageSen
             mediaUrls: mirrorMediaUrls.length ? mirrorMediaUrls : undefined,
           }
         : undefined,
+      sessionKey: params.mirror?.sessionKey,
     });
 
     return {