fix(flutter): 回退底部导航为四槽

lib/core/theme/app_colors.dart

@@ -42,11 +42,6 @@ abstract final class AppColors {
   /// 底部导航底色。
   static const bar = Color(0xFFFFFDFB);
 
-  /// 中央操作按钮渐变。
-  static const navCenterStart = Color(0xFFFF9A3D);
-  static const navCenterEnd = Color(0xFFFF6A00);
-  static const navCenterShadow = Color(0x33FF7A1A);
-
   /// 卡片轻阴影。
   static const cardShadow = Color(0x14FF8A3D);
 

lib/core/theme/app_dimens.dart

@@ -47,8 +47,6 @@ abstract final class AppDimens {
 
   static const double navHeight = 64;
   static const double navIcon = 20;
-  static const double navCenter = 56;
-  static const double navCenterIcon = 28;
   static const double progressHeight = 3;
   static const double progressRadius = 2;
   static const double progressLineHeight = 3;

lib/core/widgets/app_bottom_nav.dart

@@ -26,37 +26,21 @@ class AppBottomNavItem {
   final bool selected;
 }
 
-/// 底部导航中央操作按钮。
-class AppBottomNavCenterAction {
-  const AppBottomNavCenterAction({
-    required this.label,
-    required this.onTap,
-    this.key = const Key('nav-center-action'),
-  });
-
-  final Key key;
-  final String label;
-  final VoidCallback onTap;
-}
-
-/// 全局五槽底部导航。
+/// 四槽底部导航，仅做浅色暖橙视觉换肤。
 class AppBottomNav extends StatelessWidget {
   const AppBottomNav({
     super.key,
     required this.items,
-    this.centerAction,
     this.backgroundColor = AppColors.bar,
     this.barKey,
   });
 
   final List<AppBottomNavItem> items;
-  final AppBottomNavCenterAction? centerAction;
   final Color backgroundColor;
   final Key? barKey;
 
   @override
   Widget build(BuildContext context) {
-    final action = centerAction;
     return ClipRect(
       child: BackdropFilter(
         filter: ImageFilter.blur(sigmaX: 20, sigmaY: 20),
@@ -69,21 +53,9 @@ class AppBottomNav extends StatelessWidget {
               color: backgroundColor.withValues(alpha: 0.95),
               border: const Border(top: BorderSide(color: AppColors.border)),
             ),
-            child: action == null
-                ? Row(
-                    children: [
-                      for (final item in items) _NavDestination(item: item),
-                    ],
-                  )
-                : Row(
-                    children: [
-                      for (final item in items.take(2))
-                        _NavDestination(item: item),
-                      Expanded(child: _CenterDestination(action: action)),
-                      for (final item in items.skip(2))
-                        _NavDestination(item: item),
-                    ],
-                  ),
+            child: Row(
+              children: [for (final item in items) _NavDestination(item: item)],
+            ),
           ),
         ),
       ),
@@ -143,53 +115,3 @@ class _NavDestination extends StatelessWidget {
     ),
   );
 }
-
-class _CenterDestination extends StatelessWidget {
-  const _CenterDestination({required this.action});
-
-  final AppBottomNavCenterAction action;
-
-  @override
-  Widget build(BuildContext context) {
-    return Center(
-      child: Semantics(
-        button: true,
-        label: action.label,
-        child: Material(
-          color: Colors.transparent,
-          shape: const CircleBorder(),
-          clipBehavior: Clip.antiAlias,
-          child: Ink(
-            width: AppDimens.navCenter,
-            height: AppDimens.navCenter,
-            decoration: const BoxDecoration(
-              shape: BoxShape.circle,
-              gradient: LinearGradient(
-                begin: Alignment.topLeft,
-                end: Alignment.bottomRight,
-                colors: [AppColors.navCenterStart, AppColors.navCenterEnd],
-              ),
-              boxShadow: [
-                BoxShadow(
-                  color: AppColors.navCenterShadow,
-                  blurRadius: 14,
-                  offset: Offset(0, 5),
-                ),
-              ],
-            ),
-            child: InkWell(
-              key: action.key,
-              customBorder: const CircleBorder(),
-              onTap: action.onTap,
-              child: const Icon(
-                Icons.add_rounded,
-                color: AppColors.onPrimary,
-                size: AppDimens.navCenterIcon,
-              ),
-            ),
-          ),
-        ),
-      ),
-    );
-  }
-}

lib/pages/discover/discover_view.dart

@@ -340,10 +340,6 @@ class _DiscoverPageState extends State<DiscoverPage> {
   }
 
   Widget _bottomNav(AppLocalizations l10n) => AppBottomNav(
-    centerAction: AppBottomNavCenterAction(
-      label: l10n.createTab,
-      onTap: () => _act(DiscoverPageAction.create),
-    ),
     items: [
       AppBottomNavItem(
         tabKey: const Key('discover-nav-home'),

lib/pages/home/home_view.dart

@@ -195,10 +195,6 @@ class _HomeTabsState extends State<_HomeTabs> {
   Widget _nav(BuildContext context, AppLocalizations l10n) {
     return AppBottomNav(
       barKey: const Key('home-tabs-bar'),
-      centerAction: AppBottomNavCenterAction(
-        label: l10n.createTab,
-        onTap: () => _selectTab(context, 2),
-      ),
       items: [
         _navItem(context, l10n, 0),
         _navItem(context, l10n, 1),

lib/pages/mine/mine_view.dart

@@ -242,10 +242,6 @@ class _MyPageState extends State<MyPage> {
 
   Widget _bottomNav(AppLocalizations l10n) {
     return AppBottomNav(
-      centerAction: AppBottomNavCenterAction(
-        label: l10n.createTab,
-        onTap: () => _act(MyPageAction.create),
-      ),
       items: [
         AppBottomNavItem(
           tabKey: const Key('mine-nav-home'),