🎨 Palette: Improve accessibility of chat navigation buttons

[thirdeyenation]

💡 What: Added aria-label attributes to the chat navigation icon-only buttons and explicitly set aria-hidden=\"true\" on their inner ligature <span> elements.
🎯 Why: Screen readers will no longer confusingly read the raw material symbol ligature text (like 'vertical_align_top' or 'keyboard_arrow_up').
📸 Before/After: Visual presentation is unchanged.
♿ Accessibility: Ensures that users relying on screen readers hear clear, descriptive action labels rather than ligature text.

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PR created automatically by Jules for task 7349774404962300616 started by @thirdeyenation

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