🎨 Palette: Add ARIA labels to chat navigation buttons

[thirdeyenation]

• 💡 What: Added aria-labels to the chat navigation buttons and aria-hidden="true" to the material icons in webui/index.html.
• 🎯 Why: Improves screen reader accessibility by providing clear labels for icon-only buttons and preventing the screen reader from reading raw ligature text.
• 📸 Before/After: N/A (non-visual change)
• ♿ Accessibility: Improved screen reader navigation for the chat area.

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PR created automatically by Jules for task 7285988993142749338 started by @thirdeyenation

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