feat: 实现导航页基础功能

- 添加导航条目和分类数据模型
- 实现导航卡片网格展示
- 支持点击卡片打开链接
- 添加主题样式（渐变色、卡片阴影）
- 区分系统默认和自定义条目
- 添加分类统计信息"

frontend/test/features/home/presentation/home_page_test.dart

@@ -8,15 +8,11 @@ import 'package:frontend/features/home/data/home_repository.dart';
 import 'package:frontend/features/home/data/mock_home_data.dart';
 import 'package:frontend/features/home/data/mock_home_repository.dart';
 import 'package:frontend/features/home/domain/models/home_data.dart';
-import 'package:frontend/features/home/domain/models/link_item.dart';
-import 'package:frontend/features/home/domain/models/link_section.dart';
-import 'package:frontend/features/home/domain/models/nav_node.dart';
 import 'package:frontend/features/home/domain/models/submit_site_draft.dart';
 import 'package:frontend/features/home/presentation/pages/home_page.dart';
 import 'package:frontend/features/home/presentation/widgets/link_card.dart';
 import 'package:frontend/features/home/presentation/widgets/link_section_view.dart';
 import 'package:frontend/features/home/presentation/widgets/sidebar_nav.dart';
-import 'package:frontend/features/home/presentation/widgets/site_form_dialog.dart';
 
 import '../../../helpers/fake_url_opener.dart';
 
@@ -382,197 +378,18 @@ void main() {
   });
 
   group('提交网站', () {
-    testWidgets('点侧栏底部按钮打开表单；提交成功后刷新一次并提示', (WidgetTester tester) async {
-      final _RecordingRepository repository = _RecordingRepository();
-      // 表单比默认视口高，用大一点的窗口，免得字段在屏幕外点不到。
-      await pumpPage(
-        tester,
-        size: const Size(1000, 1200),
-        repository: repository,
-      );
-      expect(repository.fetches, 1);
-
-      await tester.tap(navText('提交网站'));
-      await tester.pumpAndSettle();
-      expect(find.text('网站名称'), findsOneWidget);
-      expect(find.text('提交的网站会放在你自己的分组里，不会进内置分类。'), findsOneWidget);
-
-      // 页面里除了表单还有顶部搜索框，这里限定在对话框内部找输入框。
-      Finder field(int index) => find
-          .descendant(
-            of: find.byType(SiteFormDialog),
-            matching: find.byType(TextField),
-          )
-          .at(index);
-
-      await tester.enterText(field(0), 'Hugging Face');
-      await tester.enterText(field(1), 'https://huggingface.co');
-      await tester.enterText(field(3), 'AI 工具');
-      await tester.pump();
-
-      await tester.tap(find.text('提交'));
-      await tester.pumpAndSettle();
-
-      expect(repository.submitted, hasLength(1));
-      expect(repository.submitted.single.group, 'AI 工具');
-      expect(repository.fetches, 2, reason: '提交成功后要重新拉一次数据');
-      expect(find.text('已提交，感谢'), findsOneWidget);
-      expect(find.text('网站名称'), findsNothing, reason: '对话框已经关掉');
-    });
-  });
-
-  group('编辑与删除', () {
-    testWidgets('可修改的条目能编辑，保存后刷新', (WidgetTester tester) async {
-      final _MutableRepository repository = _MutableRepository();
-      await pumpPage(
-        tester,
-        size: const Size(1000, 1200),
-        repository: repository,
-      );
-      expect(repository.fetches, 1);
-
-      await tester.tap(find.byTooltip('编辑'));
-      await tester.pumpAndSettle();
-
-      // 表单预填了现有内容，提交者字段不出现。
-      expect(find.text('编辑网站'), findsOneWidget);
-      expect(
-        tester
-            .widget<TextField>(
-              find
-                  .descendant(
-                    of: find.byType(SiteFormDialog),
-                    matching: find.byType(TextField),
-                  )
-                  .at(0),
-            )
-            .controller!
-            .text,
-        'Hugging Face',
-      );
-
-      await tester.tap(find.text('提交'));
-      await tester.pumpAndSettle();
-
-      expect(repository.updated, <String>['s-1']);
-      expect(repository.fetches, 2, reason: '保存成功后要重新拉一次数据');
-      expect(find.text('已保存'), findsOneWidget);
-    });
-
-    testWidgets('删除会先确认，确认后才真的删并刷新', (WidgetTester tester) async {
-      final _MutableRepository repository = _MutableRepository();
-      await pumpPage(
-        tester,
-        size: const Size(1000, 1200),
-        repository: repository,
-      );
-
-      await tester.tap(find.byTooltip('删除'));
-      await tester.pumpAndSettle();
-      expect(find.textContaining('确定要删除「Hugging Face」'), findsOneWidget);
-
-      // 先点取消：什么都不该发生。
-      await tester.tap(find.text('取消'));
-      await tester.pumpAndSettle();
-      expect(repository.deleted, isEmpty);
-
-      await tester.tap(find.byTooltip('删除'));
-      await tester.pumpAndSettle();
-      await tester.tap(find.text('删除'));
-      await tester.pumpAndSettle();
-
-      expect(repository.deleted, <String>['s-1']);
-      expect(repository.fetches, 2);
-      expect(find.text('已删除'), findsOneWidget);
-    });
-
-    testWidgets('内置条目没有编辑和删除入口', (WidgetTester tester) async {
+    testWidgets('点侧栏底部按钮跳到后端配的提交入口', (WidgetTester tester) async {
       await pumpPage(tester);
 
-      expect(find.byType(LinkCard), findsWidgets);
-      expect(find.byTooltip('编辑'), findsNothing);
-      expect(find.byTooltip('删除'), findsNothing);
+      await tester.tap(navText('提交网站'));
+      await tester.pump();
+
+      // 地址来自后端 `site.submitUrl`，页面不再自己弹表单。
+      expect(urlOpener.openedUrls, <String>['https://mattermost.example.com']);
     });
   });
 }
 
-/// 返回一条「用户提交」的站点（editable），并记录改删调用。
-class _MutableRepository implements HomeRepository {
-  int fetches = 0;
-  final List<String> updated = <String>[];
-  final List<String> deleted = <String>[];
-
-  static const HomeData _data = HomeData(
-    siteName: 'Suxing Nav',
-    searchHint: '输入关键字搜索全网资源...',
-    navNodes: <NavNode>[NavNode(id: 'g-1', title: 'AI 工具', editable: true)],
-    sections: <LinkSection>[
-      LinkSection(
-        id: 'g-1',
-        title: 'AI 工具',
-        items: <LinkItem>[
-          LinkItem(
-            id: 's-1',
-            title: 'Hugging Face',
-            url: 'https://huggingface.co',
-            description: '开源模型与数据集社区',
-            categoryId: 'g-1',
-            editable: true,
-          ),
-        ],
-      ),
-    ],
-  );
-
-  @override
-  Future<HomeData> fetchHomeData() async {
-    fetches++;
-    return _data;
-  }
-
-  @override
-  Future<void> submitSite(SubmitSiteDraft draft) async {}
-
-  @override
-  Future<void> updateSite(String id, SubmitSiteDraft draft) async {
-    updated.add(id);
-  }
-
-  @override
-  Future<void> deleteSite(String id) async {
-    deleted.add(id);
-  }
-}
-
-/// 记录取数次数与提交内容，用来验证页面的联调行为。
-class _RecordingRepository implements HomeRepository {
-  int fetches = 0;
-  final List<SubmitSiteDraft> submitted = <SubmitSiteDraft>[];
-  final List<String> updated = <String>[];
-  final List<String> deleted = <String>[];
-
-  @override
-  Future<HomeData> fetchHomeData() async {
-    fetches++;
-    return mockHomeData;
-  }
-
-  @override
-  Future<void> submitSite(SubmitSiteDraft draft) async {
-    submitted.add(draft);
-  }
-
-  @override
-  Future<void> updateSite(String id, SubmitSiteDraft draft) async {
-    updated.add(id);
-  }
-
-  @override
-  Future<void> deleteSite(String id) async {
-    deleted.add(id);
-  }
-}
-
 /// 数据一直不回来，用来测加载中的那一帧。
 class _PendingRepository implements HomeRepository {
   final Completer<HomeData> completer = Completer<HomeData>();