Scaffold plant app - MQTT monitoring for boiler-room equipment

Read-only monitoring/alerting for boilers, water softener, calorifiers
and pumps via a generic MQTT-topic-prefix asset model, so new
equipment can be onboarded without new ingestion code. Threshold and
stale-data alert rules with email + in-app notification.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/main.tsx

@@ -0,0 +1,10 @@
+import React from 'react'
+import ReactDOM from 'react-dom/client'
+import App from './App'
+import './index.css'
+
+ReactDOM.createRoot(document.getElementById('root')!).render(
+  <React.StrictMode>
+    <App />
+  </React.StrictMode>
+)