Add Claude Code documentation and expand .gitignore

Added CLAUDE.md with comprehensive guidance for Claude Code when working in this repository, including architecture patterns, testing conventions, and development workflows.

Expanded .gitignore to cover Ruby development artifacts (bundler, gems, coverage, RuboCop cache) and Claude Code user-specific files.

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

Co-Authored-By: Claude <[email protected]>

Author: oschwald

.gitignore

@@ -1,3 +1,33 @@
+# Editor files
 *.swp
+*~
+.DS_Store
+
+# YARD documentation
 /doc
 /.yardoc
+
+# Bundler
+/.bundle
+/vendor/bundle
+
+# Gem build artifacts
+*.gem
+/pkg
+
+# Test coverage
+/coverage
+
+# RuboCop cache
+/.rubocop-*
+
+# IDE/Editor specific
+/.idea
+/.vscode
+*.iml
+
+# Temporary files
+/tmp
+
+# Claude Code
+.claude