🎨 Palette: Add tooltip to settings icon button

[CommanderPho]

💡 What: Added a tooltip property to the settings IconButton in the main application app bar.
🎯 Why: To improve accessibility. Icon-only buttons without explicit tooltips lack semantic meaning for screen readers and don't provide hover context for visual users.
📸 Before/After: The settings icon now displays a "Settings" tooltip when hovered over or focused.
♿ Accessibility: The tooltip property in Flutter natively acts as an ARIA label equivalent, ensuring screen readers announce "Settings" when the button is focused.

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PR created automatically by Jules for task 2356697889984641088 started by @CommanderPho

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