feat: 更新 H5ShellPage 背景颜色为白色；启用安全区域设置

lib/main.dart

@@ -563,9 +563,8 @@ class _H5ShellPageState extends State<H5ShellPage> {
         }
       },
       child: Scaffold(
-        backgroundColor: _shellBackground,
+        backgroundColor: Colors.white,
         body: SafeArea(
-          top: false,
           bottom: false,
           child: Stack(
             children: [