style(nav): 对齐四 Tab 底栏布局规格

lib/core/widgets/app_bottom_nav.dart

@@ -26,30 +26,17 @@ class AppBottomNavItem {
 
 /// 四槽底部导航：纯黑背景，白色选中态，灰色未选中态。
 class AppBottomNav extends StatelessWidget {
-  const AppBottomNav({
-    super.key,
-    required this.items,
-    this.backgroundColor = AppColors.navBackground,
-    this.barKey,
-    this.dark = false,
-  });
+  const AppBottomNav({super.key, required this.items, this.barKey});
 
   final List<AppBottomNavItem> items;
-  final Color backgroundColor;
   final Key? barKey;
-  final bool dark;
 
   @override
   Widget build(BuildContext context) {
     final bar = Container(
       key: barKey,
       height: AppDimens.navHeight,
-      decoration: BoxDecoration(
-        color: dark ? AppColors.navBackground : backgroundColor,
-        border: const Border(
-          top: BorderSide(color: AppColors.navDivider, width: 0.5),
-        ),
-      ),
+      color: AppColors.navBackground,
       child: Row(
         children: [
           for (final item in items)
@@ -99,7 +86,7 @@ class _NavDestination extends StatelessWidget {
                       : unselectedColor,
                 ),
               ),
-              const SizedBox(height: 3),
+              const SizedBox(height: AppDimens.navLabelGap),
               Text(
                 item.label,
                 maxLines: 1,

lib/core/widgets/app_root_tab.dart

@@ -3,6 +3,7 @@
 import 'package:flutter/material.dart';
 
 import '../../l10n/app_localizations.dart';
+import 'app_bottom_nav.dart';
 
 /// 客户端根导航的固定顺序。
 enum AppRootTab { home, recommend, following, mine }
@@ -36,3 +37,36 @@ extension AppRootTabUi on AppRootTab {
     AppRootTab.mine => l10n.myTab,
   };
 }
+
+/// 根导航唯一入口，确保四个主页面使用完全一致的底栏配置。
+class AppRootBottomNav extends StatelessWidget {
+  const AppRootBottomNav({
+    super.key,
+    required this.selected,
+    required this.onSelected,
+    this.barKey,
+  });
+
+  final AppRootTab selected;
+  final ValueChanged<AppRootTab> onSelected;
+  final Key? barKey;
+
+  @override
+  Widget build(BuildContext context) {
+    final l10n = AppLocalizations.of(context)!;
+    return AppBottomNav(
+      barKey: barKey,
+      items: [
+        for (final tab in AppRootTab.values)
+          AppBottomNavItem(
+            tabKey: tab.tabKey,
+            icon: tab.icon,
+            selectedIcon: tab.selectedIcon,
+            label: tab.label(l10n),
+            selected: tab == selected,
+            onTap: () => onSelected(tab),
+          ),
+      ],
+    );
+  }
+}