feat: add underline expansion animation submission

[Shreeya1207]

Description

This PR adds a new submission demonstrating an Underline Expansion animation utility.

Added Effect

• underline-expansion

Files Added

• submissions/examples/ease-underline-expansion/demo.html
• submissions/examples/ease-underline-expansion/style.css
• submissions/examples/ease-underline-expansion/README.md

Demo

The demo showcases links with a smooth underline expansion effect that animates from left to right on hover. The animation provides clear visual feedback while maintaining a clean and modern appearance.

Why

Underline expansion is a popular micro-interaction used in navigation menus, documentation sites, landing pages, and interactive text elements. It enhances user engagement, improves link discoverability, and provides a polished browsing experience. This utility is lightweight, reusable, and aligns with EaseMotion CSS's philosophy of expressive and human-readable animation utilities.

Checklist

• Added files only inside submissions/
• Included demo.html
• Included style.css
• Included README.md
• One feature per PR
• Demo works without external dependencies
• Followed contribution guidelines

[github-actions]

✅ Submission Validation Passed!

Great job! All required files are present.

📁 Folder: submissions/examples/ease-underline-expansion

Files found:

• ✅ demo.html
• ✅ style.css
• ✅ README.md

🚀 Next Steps:

• The maintainer will review your PR
• Respond to any feedback if requested
• Once approved, your contribution will be merged!

Thank you for contributing to EaseMotion CSS! 🎉