Add Express server with WebSocket, CORS, and room routes

Set up the HTTP server with Express, attach Socket.IO for real-time
messaging, add CORS middleware, async error handling utility, and
REST routes for room join/leave/messages/participants.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Backend/server.js

@@ -0,0 +1,44 @@
+const http = require('http')
+const express = require('express')
+const config = require('./config')
+const createDataStore = require('./lib/datastore')
+const createRealtimeServer = require('./lib/simpleWebSocket')
+const createCorsMiddleware = require('./middleware/cors')
+const createRoomsRouter = require('./routes/rooms')
+
+const app = express()
+const server = http.createServer(app)
+
+app.use(express.json())
+app.use(createCorsMiddleware(config.clientOrigin))
+
+app.get('/health', (_req, res) => {
+  res.json({ status: 'ok', time: new Date().toISOString() })
+})
+
+async function bootstrap() {
+  try {
+    const database = await createDataStore()
+    const io = createRealtimeServer(server, {
+      clientOrigin: config.clientOrigin,
+      database,
+      onError: (message, error) => console.error(message, error),
+    })
+
+    app.use('/rooms', createRoomsRouter({ database, io }))
+
+    app.use((error, _req, res, _next) => {
+      console.error('Request failed', error)
+      res.status(500).json({ error: 'Internal server error' })
+    })
+
+    server.listen(config.port, () => {
+      console.log(`Chat backend running on http://localhost:${config.port}`)
+    })
+  } catch (error) {
+    console.error('Unable to start server:', error)
+    process.exit(1)
+  }
+}
+
+bootstrap()