feat(iios): wire the three-proof gate into the request path (§1b)

Applies the context-attestation verifier at the request boundary via a guard, so a
stolen/forged/replayed attestation is rejected before IIOS acts — while staying safe
to roll out.

- ContextAttestationGuard: if an X-Context-Attestation header is present, verify it
  (its app_id must match the actor token's app_id) → 403 on any failure; if absent,
  allow only when IIOS_REQUIRE_ATTESTATION != 1 (dev/zero-trust), else 403. The flag is
  read per-request and defaults OFF, so existing callers keep working until AppShell/
  be-crm start forwarding attestations.
- AttestationModule (@Global): provides the verifier + Prisma stores + guard, and
  dev-seeds the crm-support-widget client so locally minted attestations verify.
- Guard applied to ThreadsController + SupportController.
- Tests (5 pass, no DB): not-required-allows, required-rejects, valid, forged, replayed.

Workload/mTLS (proof #2) stays a mesh concern. Next: SDK header passthrough + demote
be-crm IiosClient to forward an attestation, then flip the flag to prove end-to-end.

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 { AttestationModule } from './platform/attestation.module';
 import { IdentityModule } from './identity/identity.module';
 import { InteractionsModule } from './interactions/interactions.module';
 import { IdempotencyModule } from './idempotency/idempotency.module';
@@ -27,6 +28,7 @@ import { DevController } from './dev/dev.controller';
   imports: [
     PrismaModule,
     PlatformModule,
+    AttestationModule,
     IdentityModule,
     InteractionsModule,
     IdempotencyModule,