style(nav): 对齐四 Tab 底栏布局规格

test/home/home_nav_ui_test.dart

@@ -85,12 +85,8 @@ void main() {
 
     final barFinder = find.byKey(const Key('home-tabs-bar'));
     final bar = tester.widget<Container>(barFinder);
-    final decoration = bar.decoration as BoxDecoration;
-    final border = decoration.border as Border;
-    // 所有页面统一深色导航。
-    expect(decoration.color, AppColors.navBackground);
-    expect(border.top.color, AppColors.navDivider);
-    expect(border.top.width, 0.5);
+    expect(bar.color, AppColors.navBackground);
+    expect(bar.decoration, isNull);
     expect(
       tester
           .widget<Text>(
@@ -158,12 +154,8 @@ void main() {
     await tester.pumpAndSettle();
     expect(haptics.selectionClicks, 1);
     final theaterBar = tester.widget<Container>(barFinder);
-    final theaterDecoration = theaterBar.decoration as BoxDecoration;
-    expect(theaterDecoration.color, AppColors.navBackground);
-    expect(
-      (theaterDecoration.border as Border).top.color,
-      AppColors.navDivider,
-    );
+    expect(theaterBar.color, AppColors.navBackground);
+    expect(theaterBar.decoration, isNull);
     await tester.tap(find.byKey(const Key('tab-recommend')));
     await tester.pumpAndSettle();
     expect(haptics.selectionClicks, 1);