docs(engine): document missing motion engine keyframes with reproducible demo

[broskell]

Summary

This PR adds a documentation submission that demonstrates and documents a gap in the current motion engine implementation.

The submission includes a reproducible demo highlighting several animation names accepted by the engine that currently have no corresponding keyframe definitions, making it easier for maintainers to verify and address the issue in a future core update.

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Why

While exploring the motion engine, I noticed that several supported animation names can be parsed successfully but do not produce visible animations due to missing keyframe definitions.

Since contributors are only allowed to submit content inside the submissions/ directory, this PR provides a self-contained documentation example instead of modifying the framework itself.

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Contents

Added a new documentation submission:

submissions/docs/engine-missing-keyframes-ks/
├── demo.html
├── style.css
└── README.md

The submission includes:

• A reproducible demonstration of the affected animations
• Documentation describing the observed behavior
• Expected vs. actual results
• Suggested direction for a future framework fix

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Notes

This PR intentionally does not modify any framework files.

It serves as a reproducible reference that maintainers can use when implementing the fix in the core library.

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Testing

• ✅ Submission follows the required directory structure
• ✅ Includes demo.html, style.css, and README.md
• ✅ Demo renders correctly in a browser
• ✅ No modifications outside the submissions/ directory

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Checklist

• Submission placed under submissions/docs/
• Includes all required files
• Original content
• No core framework modifications
• Ready for maintainer review

[SAPTARSHI-coder]

✅ Submission Validation Passed!

Great job! All required files are present and valid.

📁 Folder: submissions/docs/engine-missing-keyframes-ks

Files found:

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

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

Thank you for contributing to EaseMotion CSS! 🎉

[github-actions]

🎉 Congratulations on your PR merge, @broskell! 🚀

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[github-actions]

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🎮 Join our Discord Server!
We have an official Discord server for EaseMotion CSS! Join us to connect with other developers, seek help, discuss design choices, and share your creations in the showcase channel: Join the EaseMotion CSS Discord 💜