Enhance Doma CodeGen Plugin documentation with comprehensive guide

- Add comprehensive getting started section with step-by-step setup
- Include PostgreSQL, MySQL, and Testcontainers examples
- Document key benefits and use cases for the plugin
- Add detailed configuration reference with practical examples
- Expand template customization documentation
- Add .claude directory to .gitignore
- Update Japanese translation files

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

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

Author: nakamura-to

.gitignore

@@ -10,3 +10,4 @@
 out
 .factorypath
 /docs/**/*.mo
+/.claude