feat: 优化底部导航栏组件及初始化逻辑

- 在CommonComponents中为BottomTabBar添加了便捷初始化和最简初始化方法，简化了外部使用。
- 新增内部默认items方法，确保底部导航栏的图标资源一致性。
- 在MainPage中更新BottomTabBar的使用方式，直接传入viewModel，提升代码可读性和维护性。

yana/MVVM/CommonComponents.swift

@@ -25,6 +25,36 @@ struct BottomTabBar: View {
     var contentPadding: EdgeInsets = EdgeInsets(top: 12, leading: 0, bottom: 12, trailing: 0)
     var horizontalPadding: CGFloat = 0
     
+    // 便捷初始化：内部固定 tabs，避免外部重复声明
+    init(
+        selectedId: Binding<String>,
+        onSelect: @escaping (String) -> Void,
+        contentPadding: EdgeInsets = EdgeInsets(top: 12, leading: 0, bottom: 12, trailing: 0),
+        horizontalPadding: CGFloat = 0
+    ) {
+        self.items = BottomTabBar.defaultItems()
+        self._selectedId = selectedId
+        self.onSelect = onSelect
+        self.contentPadding = contentPadding
+        self.horizontalPadding = horizontalPadding
+    }
+    
+    // 最简初始化：直接接受 viewModel，内部处理所有逻辑
+    init(viewModel: MainViewModel) {
+        self.items = BottomTabBar.defaultItems()
+        self._selectedId = Binding(
+            get: { viewModel.selectedTab.rawValue },
+            set: { raw in
+                if let tab = MainViewModel.Tab(rawValue: raw) {
+                    viewModel.onTabChanged(tab)
+                }
+            }
+        )
+        self.onSelect = { _ in } // 保留但不再使用
+        self.contentPadding = EdgeInsets(top: 12, leading: 0, bottom: 12, trailing: 0)
+        self.horizontalPadding = 0
+    }
+    
     // 使用 BottomTabView.swift 中的图片资源名进行映射
     private func assetIconName(for item: TabBarItem, isSelected: Bool) -> String? {
         switch item.id {
@@ -37,6 +67,14 @@ struct BottomTabBar: View {
         }
     }
     
+    // 内部默认 items（与资源映射保持一致）
+    private static func defaultItems() -> [TabBarItem] {
+        return [
+            TabBarItem(id: "feed", title: "Feed", systemIconName: "list.bullet"),
+            TabBarItem(id: "me", title: "Me", systemIconName: "person.circle")
+        ]
+    }
+    
     var body: some View {
         HStack(spacing: 8) {
             ForEach(items) { item in

yana/MVVM/MainPage.swift

@@ -27,24 +27,10 @@ struct MainPage: View {
                     VStack {
                         Spacer()
                         // 底部导航栏（组件化）
-                        BottomTabBar(
-                            items: [
-                                TabBarItem(id: MainViewModel.Tab.feed.rawValue, title: MainViewModel.Tab.feed.title, systemIconName: MainViewModel.Tab.feed.iconName),
-                                TabBarItem(id: MainViewModel.Tab.me.rawValue, title: MainViewModel.Tab.me.title, systemIconName: MainViewModel.Tab.me.iconName)
-                            ],
-                            selectedId: Binding(
-                                get: { viewModel.selectedTab.rawValue },
-                                set: { raw in
-                                    if let tab = MainViewModel.Tab(rawValue: raw) {
-                                        viewModel.onTabChanged(tab)
-                                    }
-                                }
-                            ),
-                            onSelect: { _ in }
-                        )
+                        BottomTabBar(viewModel: viewModel)
                         .frame(height: 80)
                         .padding(.horizontal, 24)
-                        .padding(.bottom, 100)
+                        .padding(.bottom)
                     }
                 }.ignoresSafeArea(.all)
             }