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/pubspec.lock

@@ -75,6 +75,22 @@ packages:
     description: flutter
     source: sdk
     version: "0.0.0"
+  http:
+    dependency: "direct main"
+    description:
+      name: http
+      sha256: "87721a4a50b19c7f1d49001e51409bddc46303966ce89a65af4f4e6004896412"
+      url: "https://pub.flutter-io.cn"
+    source: hosted
+    version: "1.6.0"
+  http_parser:
+    dependency: transitive
+    description:
+      name: http_parser
+      sha256: "178d74305e7866013777bab2c3d8726205dc5a4dd935297175b19a23a2e66571"
+      url: "https://pub.flutter-io.cn"
+    source: hosted
+    version: "4.1.2"
   leak_tracker:
     dependency: transitive
     description:
@@ -192,6 +208,14 @@ packages:
       url: "https://pub.flutter-io.cn"
     source: hosted
     version: "0.7.11"
+  typed_data:
+    dependency: transitive
+    description:
+      name: typed_data
+      sha256: f9049c039ebfeb4cf7a7104a675823cd72dba8297f264b6637062516699fa006
+      url: "https://pub.flutter-io.cn"
+    source: hosted
+    version: "1.4.0"
   vector_math:
     dependency: transitive
     description: