feat(iios): socket.io Redis adapter for cross-replica realtime (P9 scaling)

Adds an opt-in RedisIoAdapter (wired in main.ts when REDIS_URL is set) so
socket.io room emits fan out across instances via Redis pub/sub — a client on
replica B now receives messages emitted by replica A. Without REDIS_URL the
in-memory adapter is kept (single-instance dev unchanged). Adds redis to
docker-compose, REDIS_URL to the env contract, and smoke-realtime-cluster.mjs
which proves cross-instance delivery fails without Redis and passes with it.
Delivery is at-least-once at N>1; clients dedupe by message id (documented).

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

packages/iios-service/src/main.ts

@@ -4,6 +4,7 @@ import { NestFactory } from '@nestjs/core';
 import { ValidationPipe } from '@nestjs/common';
 import { AppModule } from './app.module';
 import { traceMiddleware } from './observability/trace.middleware';
+import { RedisIoAdapter } from './realtime/redis-io.adapter';
 
 async function bootstrap(): Promise<void> {
   const app = await NestFactory.create(AppModule, { rawBody: true });
@@ -12,6 +13,15 @@ async function bootstrap(): Promise<void> {
     new ValidationPipe({ whitelist: true, forbidNonWhitelisted: true, transform: true }),
   );
   app.enableCors({ origin: true, credentials: true });
+
+  // Multi-replica realtime: fan socket.io room emits across instances via Redis.
+  // Opt-in — without REDIS_URL the default in-memory adapter is used (single instance).
+  if (process.env.REDIS_URL) {
+    const redisAdapter = new RedisIoAdapter(app, process.env.REDIS_URL);
+    await redisAdapter.connect();
+    app.useWebSocketAdapter(redisAdapter);
+  }
+
   const port = Number(process.env.PORT ?? 3200);
   await app.listen(port);
   // eslint-disable-next-line no-console