feat: add sitemap integration and configure site URL

- Add @astrojs/sitemap dependency and configure it in astro.config.mjs
- Set site URL and markdown theme in astro config
- Remove unused theme variables from global.css

astro.config.mjs

@@ -4,8 +4,16 @@ import tailwindcss from "@tailwindcss/vite";
 
 import react from "@astrojs/react";
 
+import sitemap from "@astrojs/sitemap";
+
 // https://astro.build/config
 export default defineConfig({
+  site: 'https://zhaoguiyang.com',
+  markdown: {
+    shikiConfig: {
+      theme: 'dracula',
+    },
+  },
   vite: {
       plugins: [tailwindcss()],
   },
@@ -19,5 +27,13 @@ export default defineConfig({
       prefixDefaultLocale: false,
     }
   },
-  integrations: [react()]
+  integrations: [react(), sitemap({
+    i18n: {
+      defaultLocale: 'en',
+      locales: {
+        en: 'en',
+        zh: 'zh'
+      },
+    },
+  })]
 });