Restore CNAME and configure custom domain

- Restore CNAME file with realcoding.blog domain
- Update _config.yml URL to https://realcoding.blog
- Attempt to reactivate custom domain after DNS changes
- GitHub Pages will validate domain and enable HTTPS when ready

Author: realcoding2003

CNAME

@@ -0,0 +1 @@
+realcoding.blog

_config.yml

@@ -1,7 +1,7 @@
 # Site settings
 title: Real Coding Blog
 description: 실무에서 배운 개발 노하우와 기술적 인사이트를 공유합니다
-url: "https://realcoding2003.github.io"
+url: "https://realcoding.blog"
 baseurl: ""
 
 # Author information