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/routes/public/mitra.chat.routes.js

@@ -1,8 +1,9 @@
 import { authenticate } from '../../plugins/auth.js'
 import { getMitraByFirebaseUid } from '../../services/mitra.service.js'
 import { acceptPairingRequest, declinePairingRequest } from '../../services/pairing.service.js'
-import { getActiveSessionsByMitra, endSession } from '../../services/session.service.js'
+import { getActiveSessionsByMitra, endSession, getMitraHistory } from '../../services/session.service.js'
 import { subscribe } from '../../plugins/valkey.js'
+import { respondToExtension } from '../../services/extension.service.js'
 
 const resolveMitra = async (request, reply) => {
   const mitra = await getMitraByFirebaseUid(request.firebaseUser.uid)
@@ -66,4 +67,27 @@ export const mitraChatRoutes = async (app) => {
     const session = await endSession(request.params.sessionId, 'mitra')
     return reply.send({ success: true, data: session })
   })
+
+  // Respond to extension request
+  app.post('/sessions/:sessionId/extend-response', { preHandler: [authenticate, resolveMitra] }, async (request, reply) => {
+    const { extension_id, accepted } = request.body || {}
+    if (!extension_id || accepted === undefined) {
+      return reply.code(400).send({
+        success: false,
+        error: { code: 'BAD_REQUEST', message: 'extension_id and accepted are required' },
+      })
+    }
+    const extension = await respondToExtension(extension_id, request.params.sessionId, request.mitra.id, accepted)
+    return reply.send({ success: true, data: extension })
+  })
+
+  // Chat history
+  app.get('/history', { preHandler: [authenticate, resolveMitra] }, async (request, reply) => {
+    const { page, limit } = request.query
+    const history = await getMitraHistory(request.mitra.id, {
+      page: page ? parseInt(page) : 1,
+      limit: limit ? parseInt(limit) : 20,
+    })
+    return reply.send({ success: true, data: history })
+  })
 }