fix: default to light mode for better initial user experience

Author: Albert-Lsk

src/layouts/Layout.astro

@@ -30,9 +30,6 @@ const { title, description = "Markdown 中文教程 - 完整指南" } = Astro.pr
         if (typeof localStorage !== 'undefined' && localStorage.getItem('theme')) {
           return localStorage.getItem('theme');
         }
-        if (window.matchMedia('(prefers-color-scheme: dark)').matches) {
-          return 'dark';
-        }
         return 'light';
       })();
       if (theme === 'dark') {