🎨 Palette: [UX improvement] Enhance Dialog component accessibility

[ivanleekk]

💡 What

Added essential ARIA attributes and focus styles to the Dialog component to improve its accessibility.

• The backdrop now has aria-hidden="true".
• The modal container now has role="dialog" and aria-modal="true".
• The icon-only close button now has an aria-label="Close dialog" and focus-visible styles for better keyboard navigation.

🎯 Why

Dialogs are critical UI elements that require proper ARIA attributes to be announced correctly by screen readers. Without these attributes, screen reader users might not realize a modal has opened or be able to easily find the close button. Furthermore, icon-only buttons always need an aria-label for assistive technologies. Adding focus-visible ensures that users navigating via keyboard can clearly see when the close button has focus.

📸 Before/After

(Visuals remain unchanged for standard pointer interactions, but keyboard focus ring is now visible on the close button, and screen reader announcements are significantly improved.)

♿ Accessibility

• Screen readers will now correctly identify the component as a modal dialog and trap context appropriately.
• The close button is now properly labeled for screen readers.
• Keyboard navigation is improved with a clear focus ring on the close button.

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PR created automatically by Jules for task 5307551743830549429 started by @ivanleekk

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