feat(recommend): 上新板块改按后端语义码判断，顶部轮播改为无缝循环

Drama 新增 tagCode，推荐页只看 NEW_ARRIVAL 这个码决定上新横滑，
不再依赖可变的标签文案；分类网格高度改为复用卡片的统一常量。
头部轮播改用虚拟无限页码，首尾相接且能反向滑，自动播放不再倒滑回第一张。

test/recommend/home_hero_carousel_test.dart

@@ -0,0 +1,83 @@
+// Author: fruit.com.cn
+
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:fruitshorts/core/data/models/home_feed.dart';
+import 'package:fruitshorts/core/theme/app_colors.dart';
+import 'package:fruitshorts/l10n/app_localizations.dart';
+import 'package:fruitshorts/pages/recommend/widgets/home_hero_carousel.dart';
+
+const List<FeedBanner> _banners = [
+  FeedBanner(id: '1', imageUrl: 'https://cdn.test/a.png'),
+  FeedBanner(id: '2', imageUrl: 'https://cdn.test/b.png'),
+];
+
+Widget _harness(List<FeedBanner> banners) {
+  return MaterialApp(
+    locale: const Locale('en'),
+    supportedLocales: AppLocalizations.supportedLocales,
+    localizationsDelegates: AppLocalizations.localizationsDelegates,
+    home: Scaffold(
+      body: HomeHeroCarousel(
+        banners: banners,
+        dramaFor: (_) => null,
+        onWatch: (_) {},
+      ),
+    ),
+  );
+}
+
+Color? _dotColor(WidgetTester tester, int index) {
+  final decoration =
+      tester
+              .widget<Container>(find.byKey(Key('home-hero-dot-$index')))
+              .decoration
+          as BoxDecoration?;
+  return decoration?.color;
+}
+
+void main() {
+  testWidgets('should_keep_looping_backwards_from_the_first_banner', (
+    tester,
+  ) async {
+    await tester.pumpWidget(_harness(_banners));
+    await tester.pumpAndSettle();
+
+    expect(_dotColor(tester, 0), AppColors.brandRed);
+
+    // 从第一张往右滑：无缝轮播应该接到最后一张，而不是被边界挡住。
+    await tester.fling(find.byType(PageView), const Offset(700, 0), 1200);
+    await tester.pumpAndSettle();
+
+    expect(_dotColor(tester, 1), AppColors.brandRed);
+    expect(_dotColor(tester, 0), isNot(AppColors.brandRed));
+  });
+
+  testWidgets('should_wrap_to_first_banner_after_last_auto_advance', (
+    tester,
+  ) async {
+    await tester.pumpWidget(_harness(_banners));
+    await tester.pumpAndSettle();
+
+    // 自动播两次：第 2 张之后应回到第 1 张，且页码继续往前走不回头。
+    await tester.pump(const Duration(milliseconds: 4600));
+    await tester.pumpAndSettle();
+    expect(_dotColor(tester, 1), AppColors.brandRed);
+
+    await tester.pump(const Duration(milliseconds: 4600));
+    await tester.pumpAndSettle();
+    expect(_dotColor(tester, 0), AppColors.brandRed);
+  });
+
+  testWidgets('should_not_loop_when_only_one_banner', (tester) async {
+    await tester.pumpWidget(
+      _harness(const [FeedBanner(id: '1', imageUrl: 'https://cdn.test/a.png')]),
+    );
+    await tester.pumpAndSettle();
+
+    expect(find.byKey(const Key('home-hero-dot-0')), findsNothing);
+    await tester.pump(const Duration(milliseconds: 6000));
+    await tester.pumpAndSettle();
+    expect(tester.takeException(), isNull);
+  });
+}