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/.maestro/scripts/force_expire_latest_payment.js

@@ -0,0 +1,21 @@
+// Force-expire the latest pending payment_session by hitting the dev-only
+// /internal/_test/force-expire-payment endpoint. Used by the Stage 3 maestro
+// flow (04_payment_expired.yaml) to drive the waiting screen into expired
+// without waiting 20 minutes.
+//
+// Strategy: query the latest pending payment_session via raw SQL through the
+// reset-phone endpoint? — actually no, we don't have an SQL surface. Instead,
+// we expose a tiny "expire-latest-pending" variant: pass `latest=true` and
+// the backend looks up the most-recent pending row.
+//
+// Reads BACKEND_INTERNAL_URL from env (Maestro injects it from the flow).
+const url = BACKEND_INTERNAL_URL || 'http://localhost:3001'
+const resp = http.post(`${url}/internal/_test/force-expire-payment`, {
+  body: JSON.stringify({ latest: true }),
+  headers: { 'Content-Type': 'application/json' },
+})
+if (resp.status !== 200) {
+  throw new Error(`force-expire-payment failed (${resp.status}): ${resp.body}`)
+}
+const data = json(resp.body)
+output.PAYMENT_ID = data.id