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"

backend/Cargo.toml

@@ -4,3 +4,14 @@ version = "0.1.0"
 edition = "2024"
 
 [dependencies]
+axum = "0.8"
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+time = { version = "0.3", features = ["formatting"] }
+tokio = { version = "1", features = ["rt-multi-thread", "macros", "net"] }
+tower-http = { version = "0.6", features = ["cors"] }
+url = "2"
+
+[dev-dependencies]
+tempfile = "3"
+tower = { version = "0.5", features = ["util"] }