Phase 4 Stage 3: payment shell (multi-screen flow)

Six new screens under /payment/* + a paymentDraftProvider holding
mode/durationId/durationMinutes/priceIDR/paymentId/isFirstSessionDiscount
across the flow. PaymentEntryScreen handles the routing decision
(eligible+enabled -> /payment/discount-paywall, else /payment/method-pick)
and clears the draft on fresh entry.

Screens:
- discount_paywall_screen: S6 first-session discount with struck-through
  gimmick price + actual price + 'mulai · Rp{actual}' CTA -> /payment/method
- method_pick_screen: chat vs call cards
- duration_pick_screen: tier list with chat|call mode toggle that resets
  the selection on swap
- payment_method_screen: QRIS-first list, posts to existing
  /api/client/payment-sessions with mode/duration/price/discount/method
- waiting_payment_screen: qr_flutter QR (encodes paymentId in mock mode),
  20-min countdown header, 3s polling for status, pauses on background
  via WidgetsBindingObserver
- payment_expired_screen: retry CTA -> /payment/method with draft retained

Status mapping: real payment_sessions.status uses 'confirmed'/'consumed'
for paid (not 'paid' as in plan) and 'expired'/'abandoned' as terminal.

home_screen 'Mulai Curhat' CTA now pushes /payment/entry.

Dev-only /internal/_test/force-expire-payment endpoint to drive Maestro
flow 04_payment_expired.yaml without waiting 20 minutes. Gated behind
NODE_ENV !== 'production'.

chat_opening_provider PricingData extended to carry Phase 4 chat/call
groups + firstSessionDiscount, back-compat with the Phase 3 shape.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

client_app/pubspec.yaml

@@ -15,8 +15,8 @@ dependencies:
   firebase_core: ^3.12.1
   firebase_messaging: ^15.2.5
 
-  # Social login (kept — activated when OAuth creds arrive; buttons hidden behind
-  # ENABLE_SOCIAL_AUTH dart-define flag until then)
+  # Social login (kept — buttons gated server-side via /api/shared/auth-providers
+  # until the corresponding OAuth env vars are set on the backend)
   google_sign_in: ^6.2.1
   sign_in_with_apple: ^6.1.0
 
@@ -38,6 +38,10 @@ dependencies:
   go_router: ^13.2.1
   flutter_local_notifications: ^21.0.0
 
+  # QR code rendering — used by the waiting-payment screen as a placeholder
+  # (mock mode encodes payment_session_id; real QR will come from Xendit later).
+  qr_flutter: ^4.1.0
+
 dev_dependencies:
   flutter_test:
     sdk: flutter