🎨 Palette: [Accessibility] Improve screen reader experience for chat navigation buttons

[thirdeyenation]

💡 What: Added aria-label to chat navigation buttons and aria-hidden="true" to their inner Material Symbol ligatures.
🎯 Why: Prevents screen readers from confusingly reading the raw ligature text (like "vertical_align_top") and provides clear action descriptions for accessibility.
📸 Before/After: N/A (strictly semantic/accessibility change).
♿ Accessibility: Improved screen reader support by correctly hiding ligatures and labeling icon-only buttons.

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PR created automatically by Jules for task 4602112972947603391 started by @thirdeyenation

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