refactor(i18n): simplify language handling across components

use Astro.currentLocale as single source of truth for language
remove manual lang prop passing to components
components now read language from document lang attribute

src/pages/zh/blog/index.astro

@@ -1,6 +1,11 @@
 ---
 import BlogLayout from '../../../layouts/BlogLayout.astro';
 import BlogList from '../../../components/BlogList.tsx';
+import { type Lang } from '@/i18n/utils';
+import { defaultLang } from '@/i18n/ui';
+
+// 使用Astro.currentLocale获取当前语言环境
+const lang = Astro.currentLocale as Lang || defaultLang;
 
 // 示例博客数据 - 暂时内联
 const blogPosts = [