🎨 Palette: Add ARIA labels to icon-only buttons

[thirdeyenation]

💡 What: Added missing aria-label attributes to icon-only action buttons across the task list, chat list, chat navigation, and file browser.
🎯 Why: To ensure screen readers can accurately interpret the function of these icon-only buttons, improving overall accessibility.
📸 Before/After: N/A (Non-visual change).
♿ Accessibility: Screen reader users will now hear the intended action (e.g., "Delete task", "Close chat") instead of a generic or missing label when focusing on these buttons.

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PR created automatically by Jules for task 18010809782925993114 started by @thirdeyenation

[google-labs-jules]

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