feat(service): P3.1 inbox tables + extract ActorResolver

IiosInboxItem + IiosInboxItemStateHistory (migration inbox-init). Extracted
resolveScope/resolveActor/ensureParticipant into a shared ActorResolver
(IdentityModule) so message + inbox layers share identity resolution; MessageService
delegates (P2 tests unchanged).

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

packages/iios-service/src/app.module.ts

@@ -1,6 +1,7 @@
 import { Module } from '@nestjs/common';
 import { PrismaModule } from './prisma/prisma.module';
 import { PlatformModule } from './platform/platform.module';
+import { IdentityModule } from './identity/identity.module';
 import { InteractionsModule } from './interactions/interactions.module';
 import { OutboxModule } from './outbox/outbox.module';
 import { ThreadsModule } from './threads/threads.module';
@@ -9,7 +10,7 @@ import { HealthController } from './health.controller';
 import { DevController } from './dev/dev.controller';
 
 @Module({
-  imports: [PrismaModule, PlatformModule, InteractionsModule, OutboxModule, ThreadsModule, MessageModule],
+  imports: [PrismaModule, PlatformModule, IdentityModule, InteractionsModule, OutboxModule, ThreadsModule, MessageModule],
   controllers: [HealthController, DevController],
 })
 export class AppModule {}