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/services/pricing.service.js

@@ -0,0 +1,54 @@
+import { getDb } from '../db/client.js'
+
+const sql = getDb()
+
+// Mock price tiers (will come from Control Center config later)
+const PRICE_TIERS = [
+  { duration_minutes: 15, price: 30000, label: '15 Menit' },
+  { duration_minutes: 30, price: 60000, label: '30 Menit' },
+  { duration_minutes: 45, price: 100000, label: '45 Menit' },
+  { duration_minutes: 60, price: 150000, label: '60 Menit' },
+  { duration_minutes: 1440, price: 250000, label: '24 Jam' },
+]
+
+export const getPriceTiers = () => PRICE_TIERS
+
+export const isValidTier = (durationMinutes, price) => {
+  return PRICE_TIERS.some(
+    (t) => t.duration_minutes === durationMinutes && t.price === price
+  )
+}
+
+export const getFreeTrial = async () => {
+  const [enabledRow] = await sql`SELECT value FROM app_config WHERE key = 'free_trial_enabled'`
+  const [durationRow] = await sql`SELECT value FROM app_config WHERE key = 'free_trial_duration_minutes'`
+  return {
+    enabled: enabledRow?.value?.value ?? false,
+    duration_minutes: durationRow?.value?.value ?? 5,
+  }
+}
+
+export const isCustomerEligibleForFreeTrial = async (customerId) => {
+  const freeTrial = await getFreeTrial()
+  if (!freeTrial.enabled) return false
+
+  const [tx] = await sql`
+    SELECT id FROM customer_transactions
+    WHERE customer_id = ${customerId}
+    LIMIT 1
+  `
+  return !tx // Eligible only if no transactions at all
+}
+
+export const getPricingForCustomer = async (customerId) => {
+  const tiers = getPriceTiers()
+  const freeTrialEligible = await isCustomerEligibleForFreeTrial(customerId)
+  const freeTrial = await getFreeTrial()
+
+  return {
+    tiers,
+    free_trial: freeTrialEligible
+      ? { eligible: true, duration_minutes: freeTrial.duration_minutes }
+      : { eligible: false },
+  }
+}