fix: update robots.txt sitemap URL to braboj.me (#136)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: braboj

astro-site/public/robots.txt

@@ -1,4 +1,4 @@
 User-agent: *
 Allow: /
 
-Sitemap: https://braboj.github.io/tutorial-git/sitemap-index.xml
+Sitemap: https://braboj.me/tutorial-git/sitemap-index.xml