fix: add keyboard focus-visible indicator to chip component

[KRUSHAL2956]

Pull Request Description

Closes #1289. Resolves keyboard focus styling of the .ease-chip checkbox labels.

Currently, the native checkbox inside .ease-chip-group is visually hidden (opacity 0, dimensions 0, position absolute, pointer-events none). Because the label acts as the visual representation of the interactive checkbox chip, keyboard users navigating with Tab do not receive any visual feedback indicating which chip has current focus.

This PR adds a :focus-visible outline indicator on the adjacent .ease-chip sibling when the hidden checkbox input receives keyboard focus, ensuring full WCAG 2.1 AA keyboard focus visibility requirements are met.

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Type of Change

• ✨ New animation / hover effect
• 🧩 New component
• 📝 Documentation improvement
• 🐛 Bug fix in an existing submission (core chip component keyboard focus state accessibility)
• Other (Accessibility improvement for keyboard navigation)

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Submission Checklist

⚠️ PRs that fail this checklist will be closed without review.
Note: This checklist is geared towards new community example submissions. Since this is a core framework bug fix resolving an open issue (#1289) in the base components directory, changes to components/ are required.

• All changes are inside submissions/examples/your-feature-name/
• Includes demo.html — self-contained, opens in browser with no server
• Includes style.css — raw CSS for the proposed feature
• Includes README.md — what it does, how to use it, why it fits EaseMotion CSS
• No changes to core/
• No changes to components/ (N/A - Core bug fix in components/chip.css)
• One feature per PR (no bundled unrelated changes)

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Feature Description

What does this add?

Adds a visible outline focus ring around interactive chips when navigated via keyboard.

How does a developer use it?

<div class="ease-chip-group">
  <input type="checkbox" id="chip1">
  <label class="ease-chip" for="chip1">Design</label>
</div>

Why does it fit EaseMotion CSS?

It improves user accessibility and keyboard navigation UX on interactive components while preserving the clean, modern look of the custom chips.

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Demo

• Demo checked (Verified using the existing components/chip-demo.html locally)

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Browser Testing

• Chrome
• Firefox
• Edge
• Safari (optional but appreciated)

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Notes for Maintainer

Tested locally with all linters (npm run lint, npm run lint:duplicates) and tests passing successfully. Visual focus ring verified on Chromium during keyboard tab navigation.

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Do not self-merge, even if you have write access.
Maximum 2 active assigned issues per contributor — unassign extras before opening a PR.

[github-actions]

📊 CSS Bundle Size Benchmark

No change in CSS bundle size. ✨