feat(service): ingest endpoint with kernel gates (P1.4)

POST /v1/interactions/ingest: fail-closed OPA gate -> resolve scope/handle(MDM,
no silent merge)/actor/channel/thread -> idempotent write of interaction+parts+
outbox CloudEvent in one tx. 4 DB-backed gate tests green (idempotent /
fail-closed / unresolved-handle / outbox event). 16 tests total.

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

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

@@ -0,0 +1,10 @@
+import { Module } from '@nestjs/common';
+import { InteractionsController } from './interactions.controller';
+import { IngestService } from './ingest.service';
+
+@Module({
+  controllers: [InteractionsController],
+  providers: [IngestService],
+  exports: [IngestService],
+})
+export class InteractionsModule {}