feat(client/purchase): 全员优惠月付特殊卡片(¥6/$1,随渠道显价)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

client/test/widget/payment_pages_test.dart

@@ -18,6 +18,13 @@ const _items = [
   PayCatalogItem(sku: 'pro_year', plan: 'pro', days: 366, priceMinor: 19999, currency: 'CNY', priceUsdtMicro: 34990000),
 ];
 
+const _itemsWithPromo = [
+  PayCatalogItem(
+      sku: 'pro_month_promo', plan: 'pro', days: 31, priceMinor: 600, currency: 'CNY',
+      priceUsdtMicro: 1000000, promo: true),
+  ..._items,
+];
+
 /// 轮询生命周期测试专用假 API:记 orderStatus / cancel 调用次数,其余按最小实现返回。
 class _PollingFakePaymentApi implements PaymentApi {
   int statusCalls = 0;
@@ -80,6 +87,29 @@ void main() {
     expect(find.text('¥199.99'), findsOneWidget);
   });
 
+  testWidgets('购买页:全员优惠月付特殊卡片(随渠道显价 + 原价划线)', (tester) async {
+    tester.view.physicalSize = const Size(800, 2400);
+    tester.view.devicePixelRatio = 1.0;
+    addTearDown(tester.view.reset);
+    await tester.pumpWidget(wrapThemed(
+      PurchaseScreen(t: t, embedded: true),
+      overrides: [payCatalogProvider.overrideWith((ref) async => _itemsWithPromo)],
+    ));
+    await tester.pumpAndSettle();
+    // 普通 3 档照旧渲染 + 1 张特殊卡片(非 PlanCard)。
+    expect(find.byType(PlanCard), findsNWidgets(3));
+    expect(find.text(t.promoBadge), findsOneWidget);
+    // 默认 USDT → 现价 \$1.00;原价(pro_month)\$4.99 同时出现在划线原价 + 下方普通
+    // pro_month PlanCard(两处同值,断言 2 处)。
+    expect(find.text('\$1.00'), findsOneWidget);
+    expect(find.text('\$4.99'), findsNWidgets(2));
+    // 切到人民币 → 现价 ¥6.00;原价 ¥29.99 同理 2 处。
+    await tester.tap(find.text(t.payChannelCny));
+    await tester.pumpAndSettle();
+    expect(find.text('¥6.00'), findsOneWidget);
+    expect(find.text('¥29.99'), findsNWidgets(2));
+  });
+
   testWidgets('支付页 crypto_address:地址/金额/复制,金额用 mono', (tester) async {
     final flow = PaymentFlowState(
       phase: PaymentPhase.awaitingPayment,