Phase 3 scaffold: chat engine (WebSocket, FCM, pricing, timer, extension, history)

- Backend: WebSocket plugin, chat/pricing/timer/extension/closure/notification services
- Client app: ChatBloc, pricing dialog, chat screen with message status, extension/goodbye flow, history
- Mitra app: MitraChatBloc, ExtensionBloc, chat screen, extension accept/reject, history
- Control center: free trial, extension timeout, early end config toggles
- DB migration: chat_messages, session_closures, session_extensions, customer_transactions tables

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/src/server.js

@@ -3,6 +3,7 @@ import { buildPublicApp } from './app.public.js'
 import { buildInternalApp } from './app.internal.js'
 import { autoOfflineStaleMitras } from './services/mitra-status.service.js'
 import { initFirebase } from './plugins/firebase.js'
+import { restoreActiveTimers } from './services/session-timer.service.js'
 
 const PUBLIC_PORT = process.env.PUBLIC_PORT || 3000
 const INTERNAL_PORT = process.env.INTERNAL_PORT || 3001
@@ -19,6 +20,9 @@ const start = async () => {
   await internalApp.listen({ port: INTERNAL_PORT, host: INTERNAL_HOST })
   console.log(`Internal API listening on ${INTERNAL_HOST}:${INTERNAL_PORT}`)
 
+  // Restore session timers for active sessions (on server restart)
+  await restoreActiveTimers()
+
   // Auto-offline mitras with stale heartbeat (every 30s)
   setInterval(async () => {
     try {