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>

apps/message-demo/package.json

@@ -0,0 +1,23 @@
+{
+  "name": "message-demo",
+  "version": "0.0.0",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "dev": "vite",
+    "build": "vite build"
+  },
+  "dependencies": {
+    "@insignia/iios-kernel-client": "workspace:*",
+    "@insignia/iios-message-web": "workspace:*",
+    "react": "^19.0.0",
+    "react-dom": "^19.0.0"
+  },
+  "devDependencies": {
+    "@types/react": "^19.0.0",
+    "@types/react-dom": "^19.0.0",
+    "@vitejs/plugin-react": "^4.3.4",
+    "typescript": "^5.7.3",
+    "vite": "^6.0.7"
+  }
+}