Enhance Gmail Monitor with dashboard and advanced settings

• Add dashboard feature with email statistics and activity chart
• Implement dark mode toggle and theme color customization
• Add font size adjustment and refresh interval settings
• Integrate email search functionality
• Improve UI/UX with animations and responsive design
• Implement multi-account support with individual email fetching
• Add notifications toggle and emails to display setting
• Refactor code for better modularity and performance
• Update dependencies to include PyQt6-Charts for dashboard visualizations