✨ Complete portfolio generation and export functionality

- Replace placeholder portfolio generation with actual HTML website creation
- Add comprehensive _generate_portfolio_html() method with professional styling
- Implement portfolio export functionality with file dialog
- Add dual button interface (Generate + Export) for portfolio workflow
- Include responsive design with light/dark mode support
- Generate statistics cards, language breakdown, and featured repositories
- Fix file dialog parameter (initialfile vs initialname)
- Support mobile-responsive layout with professional CSS

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

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

Author: dev-alt