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/projects.astro

@@ -5,13 +5,14 @@ import Footer from "@/components/Footer";
 import { useTranslations, type Lang } from "@/i18n/utils";
 import { defaultLang } from "@/i18n/ui";
 
-const lang: Lang = defaultLang;
+// 使用Astro.currentLocale获取当前语言环境
+const lang = Astro.currentLocale as Lang || defaultLang;
 const t = useTranslations(lang);
 const pageTitle = t('projects.title');
 ---
 
 <Layout title={pageTitle}>
-  <GlassHeader lang={lang} client:only="react" />
+  <GlassHeader client:only="react" />
   <main class="min-h-screen">
     <!-- Projects Hero Section -->
     <section class="py-24 relative overflow-hidden">