Phase 3 testing fixes: Fastify 5, SSE→WebSocket+FCM, enums, security, session lifecycle

- Upgrade Fastify 4→5 with all plugins (@fastify/websocket 11, cors 11, sensible 6)
- Migrate all SSE endpoints to WebSocket + FCM push (mitra chat requests, customer pairing status)
- Add flutter_local_notifications for foreground push notifications with sound
- Add splash screen to both apps (hide auth loading flash)
- Introduce constants/enums across entire codebase (no raw string literals)
- Move price tiers from hardcoded array to app_config DB (data-driven, includes 1-min test tier)
- Add session ownership validation on all shared chat routes
- Add ownership checks on endSession, respondToExtension, requestExtension
- Fix session timer: auto-complete expired/stale sessions on server restart
- Add 5-min grace period for abandoned closing sessions
- Fix extension flow: proper session_resumed handling, clearExtensionRequest, closure grace timer cleanup
- Fix chat screens: ConnectChat in initState, session status check on connect
- Fix customer expired view: 5-min countdown, closure state priority over expired state
- Fix mitra extension UI: loading spinner, disable buttons, handle EXTENSION_RESOLVED error
- Fix GoRouter navigation consistency (no more Navigator.pushNamed)
- Fix goodbye view keyboard overflow (SingleChildScrollView)
- Add active session card on customer home screen with refresh on navigate back
- Fix PricingBottomSheet extension mode (RequestExtension instead of new pairing)
- Send session_resumed to both parties on extension accept

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

backend/src/routes/public/mitra.chat.routes.js

@@ -2,8 +2,8 @@ import { authenticate } from '../../plugins/auth.js'
 import { getMitraByFirebaseUid } from '../../services/mitra.service.js'
 import { acceptPairingRequest, declinePairingRequest } from '../../services/pairing.service.js'
 import { getActiveSessionsByMitra, endSession, getMitraHistory } from '../../services/session.service.js'
-import { subscribe } from '../../plugins/valkey.js'
 import { respondToExtension } from '../../services/extension.service.js'
+import { EndedBy } from '../../constants.js'
 
 const resolveMitra = async (request, reply) => {
   const mitra = await getMitraByFirebaseUid(request.firebaseUser.uid)
@@ -23,31 +23,6 @@ const resolveMitra = async (request, reply) => {
 }
 
 export const mitraChatRoutes = async (app) => {
-  app.get('/incoming', { preHandler: [authenticate, resolveMitra] }, async (request, reply) => {
-    const mitraId = request.mitra.id
-
-    // SSE stream for incoming chat requests
-    reply.raw.writeHead(200, {
-      'Content-Type': 'text/event-stream',
-      'Cache-Control': 'no-cache',
-      'Connection': 'keep-alive',
-    })
-
-    // Keep-alive ping
-    const pingInterval = setInterval(() => {
-      reply.raw.write(': ping\n\n')
-    }, 15_000)
-
-    const unsubscribe = subscribe(`mitra:${mitraId}:requests`, (data) => {
-      reply.raw.write(`data: ${JSON.stringify(data)}\n\n`)
-    })
-
-    request.raw.on('close', () => {
-      clearInterval(pingInterval)
-      unsubscribe()
-    })
-  })
-
   app.post('/:sessionId/accept', { preHandler: [authenticate, resolveMitra] }, async (request, reply) => {
     const session = await acceptPairingRequest(request.params.sessionId, request.mitra.id)
     return reply.send({ success: true, data: session })
@@ -64,7 +39,7 @@ export const mitraChatRoutes = async (app) => {
   })
 
   app.post('/sessions/:sessionId/end', { preHandler: [authenticate, resolveMitra] }, async (request, reply) => {
-    const session = await endSession(request.params.sessionId, 'mitra')
+    const session = await endSession(request.params.sessionId, EndedBy.MITRA, request.mitra.id)
     return reply.send({ success: true, data: session })
   })