🎨 Palette: [Accessibility] Improve Dialog component screen reader support

[ivanleekk]

💡 What

Improved the accessibility of the Dialog component by adding appropriate ARIA attributes for screen readers.

🎯 Why

Screen reader users need context when interacting with custom modals. Without these attributes, screen readers may read background content when a modal is open, fail to announce the container as a dialog, or misinterpret the icon-only close button.

📸 Before/After

No visual changes.

♿ Accessibility

• Added aria-hidden="true" to the modal backdrop overlay to prevent screen readers from announcing it.
• Added role="dialog" and aria-modal="true" to the modal container to trap focus virtually and announce the element as a dialog.
• Added aria-label="Close" to the icon-only dismiss <button>.

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PR created automatically by Jules for task 7428669541806484063 started by @ivanleekk

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