🎨 Palette: Add ARIA labels to chat bottom actions

[thirdeyenation]

💡 What: Added aria-label attributes to the buttons in webui/components/chat/input/bottom-actions-bar.html.
🎯 Why: To ensure that icon-only buttons (like 'Nudge' on mobile) and dynamic state buttons ('Pause/Resume Agent') provide clear accessible names to screen reader users, improving overall keyboard and screen reader accessibility.
📸 Before/After: No visual changes.
♿ Accessibility: Added :aria-label and aria-label for screen reader support on Pause/Resume and Nudge buttons.

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PR created automatically by Jules for task 12367060039930692792 started by @thirdeyenation

[google-labs-jules]

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