🎨 Palette: [Accessibility] Improve icon-only button screen reader support

[thirdeyenation]

💡 What: Added explicit aria-label attributes to icon-only buttons across the chat navigation, message queue, and task list components. Added aria-hidden="true" to the inner <span class="material-symbols-outlined"> elements.
🎯 Why: Without aria-label, screen readers cannot announce the button's purpose to users. Without aria-hidden="true", screen readers will erroneously read out the raw ligature text (e.g., "delete_sweep") instead of the button's intended action, causing confusion for users navigating via keyboard and screen readers.
📸 Before/After: Visual presentation remains identical. Semantic HTML improved.
♿ Accessibility: Improves screen reader compatibility for multiple interactive elements by explicitly labeling controls and hiding decorative ligature text from accessibility trees.

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PR created automatically by Jules for task 5782302996457941854 started by @thirdeyenation

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