Add Web Animation API demo

[Harlov19]

Description

This PR adds a Web Animation API demo to the WebAPIs Playground.
It animates a colored box using keyframes, looping, and direction.
The demo works in vanilla JavaScript and provides a live preview for supported browsers.

Fixes #196

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• Ran the demo locally using npm run dev and confirmed the animation works.
• Verified browser support using the hasSupport() check; unsupported browsers show a warning message.
• Tested in multiple modern browsers (Chrome, Edge, Firefox).

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

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