🎨 Palette: Add ARIA labels to icon-only buttons

[thirdeyenation]

💡 What: Added aria-label attributes and aria-hidden="true" on internal icons to icon-only buttons across the chat navigation, tasks list, and chats list components.
🎯 Why: Improves accessibility for screen readers by ensuring icon-only buttons announce their action and preventing screen readers from reading raw ligature text.
📸 Before/After: N/A (Non-visual change).
♿ Accessibility: Added aria-label to matches title attributes on buttons and added aria-hidden="true" to internal <span class="material-symbols-outlined"> tags.

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PR created automatically by Jules for task 7325235854730310484 started by @thirdeyenation

[google-labs-jules]

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