适配平板

lib/widgets/detail_placeholder.dart

@@ -0,0 +1,31 @@
+import 'package:flutter/material.dart';
+
+/// Master-Detail 布局中右侧详情区的空白占位
+class DetailPlaceholder extends StatelessWidget {
+  final String message;
+  final IconData icon;
+
+  const DetailPlaceholder({
+    super.key,
+    this.message = '选择一条记录查看详情',
+    this.icon = Icons.touch_app_outlined,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    final colors = Theme.of(context).colorScheme;
+    return Center(
+      child: Column(
+        mainAxisSize: MainAxisSize.min,
+        children: [
+          Icon(icon, size: 64, color: colors.onSurface.withValues(alpha: 0.12)),
+          const SizedBox(height: 16),
+          Text(message,
+              style: TextStyle(
+                  fontSize: 15,
+                  color: colors.onSurface.withValues(alpha: 0.25))),
+        ],
+      ),
+    );
+  }
+}