fix: QR 预览优化 — 移除虚线边框/圆角/padding，专业白底+微阴影

- 去掉 border-dashed / rounded-2xl / p-4（干扰扫描）
- 纯白容器 + shadow-sm，干净专业
- svgToDataUrl 改用 TextEncoder（替代废弃的 unescape）

Co-Authored-By: Claude <noreply@anthropic.com>

gui/src-frontend/src/components/QrPreview.tsx

@@ -1,10 +1,12 @@
 import { useMemo } from 'react';
 import { useQrState } from '../store/qrContext';
 
-/** 将 SVG 字符串转为安全的 data URL（<img> 标签中浏览器会阻止 SVG 内的脚本执行） */
+/** SVG 字符串 → data URL（安全渲染，img 上下文阻止脚本执行） */
 function svgToDataUrl(svg: string): string {
-  const encoded = btoa(unescape(encodeURIComponent(svg)));
-  return `data:image/svg+xml;base64,${encoded}`;
+  // TextEncoder 比 btoa(unescape(...)) 更可靠，正确支持 UTF-8
+  const bytes = new TextEncoder().encode(svg);
+  const binStr = Array.from(bytes, (b) => String.fromCharCode(b)).join('');
+  return `data:image/svg+xml;base64,${btoa(binStr)}`;
 }
 
 export default function QrPreview() {
@@ -15,10 +17,13 @@ export default function QrPreview() {
     [state.preview?.svg],
   );
 
+  const containerCls =
+    'w-64 h-64 flex items-center justify-center bg-white rounded-xl shadow-sm';
+
   if (!svgDataUrl) {
     return (
       <div className="flex flex-col items-center justify-center gap-3 text-gray-400">
-        <div className="w-64 h-64 border-2 border-dashed border-gray-300 dark:border-gray-700 rounded-2xl flex items-center justify-center bg-white/50 dark:bg-gray-800/50">
+        <div className={`${containerCls} border border-gray-200`}>
           {state.loading ? (
             <span className="text-sm animate-pulse">生成中...</span>
           ) : (
@@ -31,16 +36,18 @@ export default function QrPreview() {
 
   return (
     <div className="flex flex-col items-center gap-3">
-      {/* SVG 转为 data URL 通过 <img> 渲染，浏览器在 img 上下文中阻止脚本执行 */}
-      <img
-        src={svgDataUrl}
-        alt="QR 码"
-        className="w-64 h-64 border-2 border-dashed border-gray-300 dark:border-gray-700 rounded-2xl p-4 bg-white dark:bg-white qr-preview"
-      />
-      <div className="flex gap-3 text-xs text-gray-500 dark:text-gray-400">
-        <span>版本: {state.preview!.version}</span>
+      {/* 纯白背景 + 微阴影，无边框/圆角干扰扫描 */}
+      <div className={containerCls}>
+        <img
+          src={svgDataUrl}
+          alt="QR 码"
+          className="w-60 h-60"
+        />
+      </div>
+      <div className="flex gap-3 text-xs text-gray-400">
+        <span>版本 {state.preview!.version}</span>
         <span>{state.preview!.size}×{state.preview!.size}</span>
-        <span>掩码: {state.preview!.mask}</span>
+        <span>掩码 {state.preview!.mask}</span>
       </div>
     </div>
   );