fix: 移动端刷新页面后主题回退的问题

在 index.html 添加内联 script，Vue 启动前从 localStorage 读取主题
并设置 data-theme 属性，消除 Pinia store 初始化时序导致的闪烁

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

frontend/index.html

@@ -6,6 +6,14 @@
     <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no" />
     <title>企迹 - 政企周报管理系统</title>
 
+    <!-- Apply saved theme before page render to prevent flash -->
+    <script>
+      (function() {
+        var theme = localStorage.getItem('theme') || 'editorial';
+        document.documentElement.setAttribute('data-theme', theme);
+      })();
+    </script>
+
     <!-- Preconnect to Google Fonts origins for faster font loading -->
     <link rel="preconnect" href="https://fonts.googleapis.com">
     <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>