🎨 Palette: Add tooltipText to search back button

[dlukt]

💡 What: Added android:tooltipText to the search back ImageButton in the Discover fragment to mirror its contentDescription.
🎯 Why: To provide visual feedback (tooltips) when hovering with a mouse/stylus or long-pressing the button, making the UI more intuitive.
♿ Accessibility: Aligns with API 26+ best practices for icon-only buttons to provide additional context beyond screen readers.

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PR created automatically by Jules for task 3387767949145290081 started by @dlukt

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