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>

backend/src/routes/internal/_test.routes.js

@@ -38,4 +38,43 @@ export const internalTestRoutes = async (fastify) => {
     }
     return { ok: true, phone, dropped_customer: dropCustomer }
   })
+
+  // Force-expire a `pending` payment session (used by Maestro Stage 3 flow to
+  // drive the waiting-payment screen into the expired state without waiting
+  // 20 minutes). Sets `expires_at` to the past and status to `expired` so the
+  // next poll from the client sees the terminal state.
+  //
+  // Body shape:
+  //   { payment_id: '<uuid>' }      → expire this specific session
+  //   { latest: true }              → expire the most-recently-created pending
+  fastify.post('/force-expire-payment', async (request, reply) => {
+    const { payment_id, latest } = request.body ?? {}
+    let target
+    if (latest === true) {
+      const [row] = await sql`
+        SELECT id FROM payment_sessions
+        WHERE status = 'pending'
+        ORDER BY created_at DESC
+        LIMIT 1
+      `
+      if (!row) {
+        return reply.code(404).send({ error: 'no_pending_payment' })
+      }
+      target = row.id
+    } else if (payment_id) {
+      target = payment_id
+    } else {
+      return reply.code(400).send({ error: 'payment_id or latest:true required in body' })
+    }
+    const [updated] = await sql`
+      UPDATE payment_sessions
+      SET status = 'expired', expires_at = NOW() - INTERVAL '1 minute'
+      WHERE id = ${target} AND status = 'pending'
+      RETURNING id, status
+    `
+    if (!updated) {
+      return reply.code(404).send({ error: 'no_pending_payment_for_id', payment_id: target })
+    }
+    return { ok: true, ...updated }
+  })
 }