CI : CNAME 설정 추가 (book.openinfra-kr.org)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: ppiyakk2

.github/workflows/publish.yml

@@ -27,3 +27,4 @@ jobs:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: ./docs
           publish_branch: gh-pages
+          cname: book.openinfra-kr.org