feat(service): P2.2 MessageService — native send + receipts/unread + traceId

openThread (create-or-join), send (idempotent, bumps other participants' unread,
message.sent outbox event, traceId DB->event), markRead (READ receipt + unread
reset), contentRef attachment placeholder. Adds messageSent to contracts events.
5 DB-backed tests green; 24 total.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/iios-service/src/messaging/message.module.ts

@@ -0,0 +1,8 @@
+import { Module } from '@nestjs/common';
+import { MessageService } from './message.service';
+
+@Module({
+  providers: [MessageService],
+  exports: [MessageService],
+})
+export class MessageModule {}