feat(iios): idempotency-command ledger + IdempotencyService (P9)

Adds the doc-mandated IiosIdempotencyCommand table + a reusable
IdempotencyService.run() that writes IN_FLIGHT at command start, replays the
cached response on a same-key/same-body retry, rejects a same-key/different-body
reuse (409), and retries a FAILED command. Tenant-scoped via
@@unique([scopeId, commandName, idempotencyKey]) (KG-02/KG-06).

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

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

@@ -3,6 +3,7 @@ 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 { IdempotencyModule } from './idempotency/idempotency.module';
 import { OutboxModule } from './outbox/outbox.module';
 import { ThreadsModule } from './threads/threads.module';
 import { MessageModule } from './messaging/message.module';
@@ -23,6 +24,7 @@ import { DevController } from './dev/dev.controller';
     PlatformModule,
     IdentityModule,
     InteractionsModule,
+    IdempotencyModule,
     OutboxModule,
     ThreadsModule,
     MessageModule,