🎨 Palette: Add ARIA labels and hide ligatures for sidebar tasks/chats icon buttons

[thirdeyenation]

💡 What: Added aria-label attributes to the "View task details", "Clear task chat", "Delete task", "New Chat", and "Close chat" icon-only buttons in the sidebar. Added aria-hidden="true" to their inner material-symbols-outlined span elements.
🎯 Why: Icon-only buttons without accessible labels are difficult for screen-reader users to understand. Hiding the ligature text ensures screen readers do not read the text node inside the material symbol (e.g., reading "delete_sweep" verbatim).
📸 Before/After: Verified visual output using a playwright script, UI looks functionally identical but with accessibility tags added in HTML.
♿ Accessibility: Ensures that screen reader users can understand and interact with the primary task and chat actions in the sidebar.

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PR created automatically by Jules for task 6392804782930642057 started by @thirdeyenation

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