refactor: 重构 QrCodePreview 组件，继承 HTMLDiv 属性并统一 shadcn 样式

- 组件改为继承 `React.HTMLAttributes<HTMLDivElement>`，支持外部传入 className 和事件
- 使用 `cn()` 函数合并外部类名
- 空白状态改用 `border border-dashed` 和更浅的 `bg-muted/40` 背景
- 正常状态改为纯白背景柔边圆角容器包裹二维码，确保暗黑模式下黑白对比度
- 下载/复制按钮完全对齐 shadcn 的 Outline 与 Default 样式规范
- 更新测试用例中的 alt 文本为 "QR Code Preview"

components/QrCodePreview.tsx

@@ -1,7 +1,10 @@
-import { Download, Copy } from 'lucide-react';
+import React from 'react';
+import { Copy, Download } from 'lucide-react';
 import { useLazyTranslation } from '@/utils/useLazyTranslation';
+import { cn } from '@/lib/utils'; // 1. 引入标准的 shadcn 工具函数
 
-interface QrCodePreviewProps {
+// 继承原生 HTML Div 属性，方便外部无缝扩充类名或监听事件
+interface QrCodePreviewProps extends React.HTMLAttributes<HTMLDivElement> {
   /** 二维码 Data URL */
   qrCodeDataUrl: string;
   /** 下载回调 */
@@ -10,39 +13,72 @@ interface QrCodePreviewProps {
   onCopy: () => void;
 }
 
-const QrCodePreview = ({ qrCodeDataUrl, onDownload, onCopy }: QrCodePreviewProps) => {
+const QrCodePreview = ({
+  qrCodeDataUrl,
+  onDownload,
+  onCopy,
+  className,
+  ...props
+}: QrCodePreviewProps) => {
   const { t } = useLazyTranslation('qrCode');
 
+  // 空状态下的虚线骨架屏
   if (!qrCodeDataUrl) {
     return (
-      <div className="flex flex-col justify-center items-center min-h-[200px] border-2 border-dashed border-input rounded-xl p-4 bg-muted">
-        <span className="text-sm text-muted-foreground text-center">
-          {t('qrCode:qrCodeWillShow')}
-        </span>
+      <div
+        className={cn(
+          'flex flex-col justify-center items-center min-h-[200px] border border-dashed border-input rounded-xl p-4 bg-muted/40',
+          className,
+        )}
+        {...props}
+      >
+        <p className="text-sm text-muted-foreground text-center">{t('qrCode:qrCodeWillShow')}</p>
       </div>
     );
   }
 
   return (
-    <div className="flex flex-col justify-center items-center min-h-[200px] border-2 border-dashed border-input rounded-xl p-4 bg-muted">
-      <div className="flex flex-col items-center w-full">
-        <img src={qrCodeDataUrl} alt="QR Code" className="w-[250px] h-[250px] block" />
-        <div className="flex gap-2 mt-4">
+    <div
+      className={cn(
+        'flex flex-col justify-center items-center min-h-[200px] border border-input rounded-xl p-6 bg-muted/40',
+        className,
+      )}
+      {...props}
+    >
+      <div className="flex flex-col items-center w-full max-w-xs">
+        {/*
+          2. 二维码容器适配：
+          在暗黑模式下，纯黑白的二维码如果直接暴露在暗色背景下，会导致手机摄像头极难识别。
+          通过裹一层 bg-white 和 p-3，确保黑白对比度绝对安全，同时加入 shadow 增强卡片感。
+        */}
+        <div className="p-3 bg-white rounded-lg shadow-sm border border-border/40">
+          <img
+            src={qrCodeDataUrl}
+            alt="QR Code Preview"
+            className="w-56 h-56 max-w-full object-contain block animate-in fade-in duration-300"
+          />
+        </div>
+
+        {/* 3. 按钮群全面向 shadcn 官方 Button 视觉规范对齐 */}
+        <div className="flex w-full gap-2 mt-5">
+          {/* 下载按钮：使用标准的次要按钮风格 (Outline) */}
           <button
             type="button"
             onClick={onDownload}
-            className="flex items-center gap-2 px-4 py-2 text-sm font-medium text-green-600 bg-background border border-green-600 rounded-lg hover:bg-green-500/10 transition-colors"
+            className="flex-1 inline-flex h-9 items-center justify-center gap-2 px-3 text-sm font-medium rounded-md border border-input bg-background shadow-sm transition-colors hover:bg-accent hover:text-accent-foreground focus-visible:outline-none focus-visible:ring-1 focus-visible:ring-ring"
           >
-            <Download className="w-4 h-4" />
-            {t('qrCode:downloadButton')}
+            <Download className="w-4 h-4 text-muted-foreground" />
+            <span className="truncate">{t('qrCode:downloadButton')}</span>
           </button>
+
+          {/* 复制按钮：使用标准的主要行动按钮风格 (Default) */}
           <button
             type="button"
             onClick={onCopy}
-            className="flex items-center gap-2 px-4 py-2 text-sm font-medium text-white bg-green-600 rounded-lg hover:bg-green-700 transition-colors"
+            className="flex-1 inline-flex h-9 items-center justify-center gap-2 px-3 text-sm font-medium rounded-md bg-primary text-primary-foreground shadow transition-colors hover:bg-primary/90 focus-visible:outline-none focus-visible:ring-1 focus-visible:ring-ring"
           >
             <Copy className="w-4 h-4" />
-            {t('qrCode:copyQrButton')}
+            <span className="truncate">{t('qrCode:copyQrButton')}</span>
           </button>
         </div>
       </div>