feat: enhance SEO with meta tags and sitemap, add DocumentMeta component

public/robots.txt

@@ -0,0 +1,4 @@
+User-agent: *
+Allow: /
+
+Sitemap: https://ark-library.com/sitemap.xml

public/site.webmanifest

@@ -0,0 +1,17 @@
+{
+  "name": "ARK 资料库",
+  "short_name": "ARK Library",
+  "description": "ARK 官方数据库集中整理官方教材、公告、视频、图片与常用文件，帮助社区快速找到可信资料。",
+  "start_url": "/",
+  "display": "standalone",
+  "background_color": "#08070c",
+  "theme_color": "#08070c",
+  "icons": [
+    {
+      "src": "/assets/ark-mark.png",
+      "sizes": "512x512",
+      "type": "image/png",
+      "purpose": "any maskable"
+    }
+  ]
+}

public/sitemap.xml

@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
+  <url>
+    <loc>https://ark-library.com/</loc>
+  </url>
+  <url>
+    <loc>https://ark-library.com/browse</loc>
+  </url>
+  <url>
+    <loc>https://ark-library.com/categories</loc>
+  </url>
+  <url>
+    <loc>https://ark-library.com/official-recommendations</loc>
+  </url>
+  <url>
+    <loc>https://ark-library.com/about</loc>
+  </url>
+</urlset>