🎨 Enhance badge export functionality and UI styling

[BrunoV21]

📝 Summary

This pull request introduces significant improvements to the badge export feature in GitRecap, including new customization options, visual enhancements, and code refactoring for better maintainability. The changes focus on improving the visual appeal, usability, and consistency of the badge export functionality.

✨ Features

• Added export functionality to save recap summaries as PNG images or HTML badges
• Implemented theme selector with dark, light, and default options for badge export customization

🐞 Bug Fixes

• Fixed authentication flow by moving GitHub username assignment from repo fetch to PAT authorization
• Wrapped dummyOutput in a div for improved styling and layout consistency

⚙️ Improvements

• Updated badge design with warm color scheme and improved layout for better visual appeal
• Changed badge aspect ratio from 4:3 to 16:10 for better content presentation
• Increased title font size and updated font family to Maus with CDN link
• Updated button and theme option colors for improved visibility and consistency
• Updated badge gradient and background colors for improved visual consistency
• Removed export button borders and shadows, replaced button element with Button component
• Removed borders, border-radius, and box-shadow from theme selector and export option buttons
• Changed button text color from white to black for improved contrast
• Refactored API to return username from store_fetcher and simplify external_signup response handling