feat(demo): P2.7 Vite React two-pane realtime demo + dev token endpoint (P2 complete)

apps/message-demo: Alice creates a thread, Bob joins; live two-way chat, typing,
read receipts (useMessages now exposes reads[]). Dev-only /v1/dev/token endpoint
(gated by IIOS_DEV_TOKENS) so the browser can auth. .env autoloaded (dotenv).
Realtime smoke script passes end-to-end (message + unread + receipt).

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

packages/iios-service/src/main.ts

@@ -1,3 +1,4 @@
+import 'dotenv/config';
 import 'reflect-metadata';
 import { NestFactory } from '@nestjs/core';
 import { ValidationPipe } from '@nestjs/common';