feat(templates): T6 controller + DTOs + module wiring

POST /v1/templates/send (render→queue) and /preview (render only). OPA-gated in
the sender: iios.template.send, and iios.template.send.inline for ad-hoc HTML
(arbitrary markup to a customer is riskier than a reviewed stored template).
Scope resolved from the caller's principal. TemplateModule registered in AppModule.

Verified over HTTP against a local boot: preview + send of the seeded
payment.receipt (SENT via sandbox, provenance persisted), XSS name escaped,
idempotent replay → 1 row, unknown key 404, bad channel/no-source/no-auth 400.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

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

@@ -10,6 +10,7 @@ import { OutboxModule } from './outbox/outbox.module';
 import { ThreadsModule } from './threads/threads.module';
 import { MessageModule } from './messaging/message.module';
 import { InboxModule } from './inbox/inbox.module';
+import { TemplateModule } from './templates/template.module';
 import { MediaModule } from './media/media.module';
 import { NotificationModule } from './notifications/notification.module';
 import { SupportModule } from './support/support.module';
@@ -37,6 +38,7 @@ import { DevController } from './dev/dev.controller';
     ThreadsModule,
     MessageModule,
     InboxModule,
+    TemplateModule,
     MediaModule,
     NotificationModule,
     SupportModule,