chore: exclude .claude and CLAUDE.md from R package build

- Add .claude directory to .Rbuildignore
- Add CLAUDE.md file to .Rbuildignore
- Fixes R CMD check NOTE about hidden files

🤖 Generated with [Claude Code](https://claude.ai/code)

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

Author: elong0527

.Rbuildignore

@@ -45,3 +45,5 @@ lib_paths
 ^r2rtf.*\.tar\.gz$
 ^r2rtf.*\.tgz$
 ^CITATION\.cff$
+^\.claude$
+^CLAUDE\.md$