Fix GUI appearance and simplify styling

- Reverted to clean, simple GUI design with better usability
- Removed overcomplicated styling that was causing visual issues
- Simplified repository panel layout with standard ttk widgets
- Cleaned up configuration panel structure
- Removed custom title bar and status bar for cleaner interface
- Fixed layout issues and improved overall functionality
- Repository addition functionality should now work properly

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

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

Author: dev-alt