feat(routing): 设置入口改分流规则下钻行 + 双形态导航

- settings_page.dart: smartRoute 布尔开关行 → 分流规则下钻行(标题 + 当前模式 pill
  + chevron),点击 desktop/tablet 切 navViewProvider 内容区下钻,mobile 全屏 push
  RoutingScreen(与 account_page.dart 的 open() 双形态导航同一范式)。
- navigation_provider.dart: 新增 NavView.routing + kSettingsSubViews 集合(登记
  settings 的下钻子页,供 shell backTarget 判断返回 settings 而非 account)。
- desktop_shell.dart/tablet_shell.dart: 内容区 switch 挂 RoutingScreen(embedded:
  true),backTarget 优先判 kSettingsSubViews → 回 settings。
- settings_ia_test.dart: 追加下钻行断言(标题+模式pill+点击导航到 RoutingScreen)。
- 重录 desktop_settings golden(唯一因本刀布局变化受影响的 golden)。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

client/test/widget/settings_ia_test.dart

@@ -10,6 +10,7 @@ import 'package:pangolin_vpn/bridge/vpn_bridge_mock.dart';
 import 'package:pangolin_vpn/bridge/vpn_bridge_provider.dart';
 import 'package:pangolin_vpn/l10n/app_text.dart';
 import 'package:pangolin_vpn/l10n/strings_zh.dart';
+import 'package:pangolin_vpn/models/routing_profile.dart';
 import 'package:pangolin_vpn/pangolin_theme.dart';
 import 'package:pangolin_vpn/screens/settings_page.dart';
 import 'package:pangolin_vpn/services/token_store.dart';
@@ -18,6 +19,8 @@ import 'package:pangolin_vpn/shell/home_shell.dart';
 import 'package:pangolin_vpn/state/app_providers.dart';
 import 'package:pangolin_vpn/state/auth_provider.dart';
 import 'package:pangolin_vpn/state/navigation_provider.dart';
+import 'package:pangolin_vpn/state/routing_provider.dart';
+import 'package:pangolin_vpn/widgets/routing_screen.dart';
 
 import '../helpers/harness.dart';
 
@@ -82,4 +85,52 @@ void main() {
       debugDefaultTargetPlatformOverride = null;
     }
   });
+
+  testWidgets('settings 连接组:smartRoute 开关被「分流规则」下钻行取代(标题+当前模式pill+chevron),点击导航到 RoutingScreen',
+      (tester) async {
+    debugDefaultTargetPlatformOverride = TargetPlatform.windows;
+    tester.view.physicalSize = const Size(920, 1400);
+    tester.view.devicePixelRatio = 1.0;
+    addTearDown(tester.view.resetPhysicalSize);
+    addTearDown(tester.view.resetDevicePixelRatio);
+    try {
+      await tester.pumpWidget(ProviderScope(
+        overrides: [
+          tokenStoreProvider.overrideWithValue(const _NullTokenStore()),
+          vpnBridgeProvider.overrideWithValue(VpnBridgeMock()),
+          appTextProvider.overrideWithValue(t),
+          navViewProvider.overrideWith((ref) => NavView.settings),
+          routingProfileProvider.overrideWith(() => _FakeRoutingNotifier(const RoutingProfile(mode: 'global'))),
+        ],
+        child: MaterialApp(
+          debugShowCheckedModeBanner: false,
+          theme: PangolinTheme.light,
+          home: const HomeShell(),
+        ),
+      ));
+      await tester.pumpAndSettle();
+
+      // 旧的 smartRoute 布尔开关行已消失。
+      expect(find.descendant(of: find.byType(SettingsPage), matching: find.text(t.smartRoute)), findsNothing);
+
+      // 新的下钻行:标题「分流规则」+ 当前模式(全局代理)pill。
+      final routingRow = find.descendant(of: find.byType(SettingsPage), matching: find.text(t.routingRulesTitle));
+      expect(routingRow, findsOneWidget);
+      expect(find.descendant(of: find.byType(SettingsPage), matching: find.text(t.routingModeGlobal)), findsOneWidget);
+
+      await tester.tap(routingRow);
+      await tester.pumpAndSettle();
+
+      expect(find.byType(RoutingScreen), findsOneWidget);
+    } finally {
+      debugDefaultTargetPlatformOverride = null;
+    }
+  });
+}
+
+class _FakeRoutingNotifier extends RoutingProfileNotifier {
+  _FakeRoutingNotifier(this._v);
+  final RoutingProfile _v;
+  @override
+  Future<RoutingProfile> build() async => _v;
 }