Refactor main.js and add new features

[A1B2C3D4E5F6G7H8I9J0164-hack]

Refactor code to improve readability and add new features including preview button, auto-save theme changes, keyboard shortcuts, and notification toasts.

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1. Fix ...
2. Refactor ...
3. Update ...
4. Implement ...

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• Fixes [Issue ticket name](Issue ticket link)
• Implements [Issue ticket name](Issue ticket link)

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[leviarista]

Hey there @A1B2C3D4E5F6G7H8I9J0164-hack Thanks for your contribution! 😊 Anyways I noticed some errors when testing some of the features, specifically when previewing the geenerated banners. Please let me know if you plan to fix those issues, if not I can do it myself too ;) Thank you

[A1B2C3D4E5F6G7H8I9J0164-hack]

i dont see any error in the code if you are seeing any issue you can change it