feat(seo): implement SEO enhancements and social media embeds

This commit introduces significant SEO improvements and enhances content embedding capabilities.

- Integrates `@nuxtjs/seo`, `@nuxtjs/sitemap`, and `@nuxtjs/robots` to boost search engine visibility.
- Configures global meta tags, including Open Graph and Twitter Cards, for richer social media sharing.
- Adds support for embedding YouTube and Facebook content directly within markdown pages.
- Introduces a new `TikTokEmbed` component for future use.

content/events/20250927-return-to-school.md

@@ -44,6 +44,16 @@ cover: "/events/20250927-return-to-school/event-photo-1.jpg"
 
 ---
 
+<iframe 
+  src="https://www.facebook.com/plugins/post.php?href=https%3A%2F%2Fwww.facebook.com%2Fstory.php%3Fstory_fbid%3D10163303061049019%26id%3D667519018"
+  class="w-full"
+  height="720" 
+  scrolling="no" 
+  frameborder="0" 
+  allowfullscreen="true" 
+  allow="autoplay; clipboard-write; encrypted-media; picture-in-picture; web-share">
+</iframe>
+
 # 午宴 • 征信录
 
 ## 乐捐名单