feat(theme) : add live theme preview system

[kavin553]

Description

Implemented a live theme preview system that allows users to preview themes in real time before applying customization changes. Added floating preview controls with Apply and Cancel actions, improved theme state handling, and enhanced the overall customization experience.

Fixes # (issue number)

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Changes Made

• Added live theme preview functionality using URL-based preview parameters.
• Implemented floating Apply/Cancel preview controls.
• Added dynamic theme state management in "app.js".
• Added responsive preview control styling in "style.css".
• Updated "index.html" to include theme preview action buttons.
• Improved user experience with instant visual feedback before saving themes.
• Ensured smooth theme switching without page reload.

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Screenshots (if applicable)

• Added screenshots showcasing:
  • Live preview mode
  • Floating preview controls
  • Different theme previews
  • Responsive mobile layout

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Checklist

• I have linked the relevant issue above.
• I have tested my changes locally.
• My code follows the project's style guidelines.

[vercel]

@kavin553 is attempting to deploy a commit to the Mayo's projects Team on Vercel.

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[kavin553]

Hi @maintainer 👋

Implemented the live theme preview feature successfully.

Highlights

• Real-time theme preview before applying customization
• Floating Apply/Cancel controls
• Instant UI updates without page reload
• Responsive and smooth user experience
• Theme restoration on cancel

Tested

• Multiple themes previewed successfully
• Mobile and desktop responsiveness verified
• No UI breaking issues observed during local testing

Please review when available. Thank you for the opportunity to contribute 🚀