feat: add comprehensive GitHub guides expansion

🆕 New Guides Added:
- GitHub Actions complete guide (CI/CD automation)
- GitHub Security comprehensive guide (enterprise security)
- GitHub Pages detailed guide (website publishing)

🔗 Navigation Improvements:
- Updated index.md with all 7 guides
- Added cross-navigation between all guides
- Enhanced learning paths for different user types
- Comprehensive learning flow diagrams

📚 Content Highlights:
- Jenkins/CircleCI migration strategies
- Enterprise security best practices
- WordPress to GitHub Pages migration
- Advanced automation workflows
- Complete external tool replacements

🎯 User Experience:
- Role-based learning recommendations
- Consistent navigation structure
- Progressive learning paths
- Cross-reference linking

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

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

features/04-github-projects.md

@@ -735,8 +735,10 @@ GitHub Projects V2を効果的に活用することで：
 ## 🔗 関連ガイド
 
 - **前のステップ**: [Pull Request編](03-pull-requests.md) - コードレビュープロセス最適化
+- **次のステップ**: [GitHub Actions編](05-github-actions.md) - プロジェクト自動化・CI/CD
 - **基礎知識**: [Issues管理編](02-issues-management.md) - タスク管理の基礎
 - **さらに基礎**: [リポジトリ基礎編](01-repository-basics.md) - 基本的なGit操作
+- **セキュリティ**: [GitHub Security編](06-github-security.md) - プロジェクトセキュリティ
 - **総合ガイド**: [GitHub完全活用ガイド](../GITHUB_COMPLETE_GUIDE.md) - 全機能の詳細解説
 
 ## 📖 学習フロー