🎨 Palette: [UX improvement] Improve chat navigation accessibility

[thirdeyenation]

💡 What: Added aria-label attributes to chat navigation buttons and aria-hidden="true" to their inner Material Symbol spans.
🎯 Why: Screen readers were confusingly reading the raw ligature text (e.g., 'vertical_align_top') instead of providing clear, accessible button names.
📸 Before/After: N/A (non-visual structural change)
♿ Accessibility: Ensures that screen reader users can understand the purpose of the scroll and navigation buttons without being confused by ligature text.

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PR created automatically by Jules for task 2659571195843592395 started by @thirdeyenation

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