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/internal/config.routes.js

@@ -101,4 +101,31 @@ export const internalConfigRoutes = async (app) => {
     const config = await setEarlyEndConfig({ mitra_enabled, customer_enabled })
     return reply.send({ success: true, data: config })
   })
+
+  // --- Price Tiers ---
+  app.get('/price-tiers', {
+    preHandler: [authenticate, attachCcUser, requirePermission('config', 'read')],
+  }, async (request, reply) => {
+    const { getPriceTiers } = await import('../../services/pricing.service.js')
+    const tiers = await getPriceTiers()
+    return reply.send({ success: true, data: tiers })
+  })
+
+  app.patch('/price-tiers', {
+    preHandler: [authenticate, attachCcUser, requirePermission('config', 'update')],
+  }, async (request, reply) => {
+    const { tiers } = request.body ?? {}
+    if (!Array.isArray(tiers) || tiers.length === 0) {
+      return reply.code(422).send({ success: false, error: { code: 'VALIDATION_ERROR', message: 'tiers must be a non-empty array' } })
+    }
+    for (const t of tiers) {
+      if (!t.duration_minutes || t.price === undefined || !t.label) {
+        return reply.code(422).send({ success: false, error: { code: 'VALIDATION_ERROR', message: 'Each tier needs duration_minutes, price, and label' } })
+      }
+    }
+    const { getDb } = await import('../../db/client.js')
+    const sql = getDb()
+    await sql`UPDATE app_config SET value = ${sql.json({ tiers })}, updated_at = NOW() WHERE key = 'price_tiers'`
+    return reply.send({ success: true, data: tiers })
+  })
 }