feat: implement SEO enhancements and sitemap generation

- Added comprehensive SEO meta tags in index.html for improved search engine visibility, including Open Graph and Twitter Card tags.
- Created a sitemap.xml for better indexing of site tools, generated automatically via a new script (generate-sitemap.ts).
- Introduced robots.txt to manage crawler access and specified sitemap location.
- Updated package.json to include a build step for sitemap generation and added tsx as a dependency.
- Documented SEO optimizations and usage instructions in a new SEO-README.md file.

public/robots.txt

@@ -0,0 +1,21 @@
+# Allow all crawlers
+User-agent: *
+Allow: /
+
+# Sitemaps
+Sitemap: https://litek.typist.cc/sitemap.xml
+
+# Common bots
+User-agent: Googlebot
+Allow: /
+
+User-agent: Bingbot
+Allow: /
+
+User-agent: Baiduspider
+Allow: /
+
+# Crawl-delay for less aggressive bots
+User-agent: *
+Crawl-delay: 1
+