🎨 Palette: Add ARIA labels to chat navigation buttons

[thirdeyenation]

💡 What: Added aria-label attributes to the chat navigation buttons (scroll to top, previous user message, next user message, scroll to bottom) in the main interface, and added aria-hidden="true" to their internal icon spans.
🎯 Why: To improve accessibility for screen readers by ensuring icon-only buttons are properly announced and preventing raw ligature text from being misread.
📸 Before/After: N/A (Visuals are unchanged, purely an accessibility improvement)
♿ Accessibility: Ensures the primary navigation actions within the chat interface are discoverable and intelligible to visually impaired users relying on screen readers.

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PR created automatically by Jules for task 10494031561768488867 started by @thirdeyenation

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