style: 统一全站深色视觉

lib/pages/auth/auth_widgets.dart

@@ -76,7 +76,7 @@ class _AuthCard extends StatelessWidget {
       decoration: BoxDecoration(
         color: AppColors.card,
         borderRadius: BorderRadius.circular(_cardRadius),
-        boxShadow: const [AppTheme.cardShadow],
+        border: Border.all(color: AppColors.border),
       ),
       child: Column(
         crossAxisAlignment: CrossAxisAlignment.stretch,