🎨 Palette: Make category rows fully clickable and accessible

[acebytes]

• 💡 What: Wrapped the CategoryRow's HStack in a Button, used .contentShape(Rectangle()) to make the empty space clickable. Added .accessibilityElement(children: .combine) and .accessibilityAddTraits(.isSelected).
• 🎯 Why: Previously, only the small checkbox icon could be tapped, which reduced usability due to a small hit target. Now the entire row can be tapped to toggle the selection, which feels like a native macOS list, while vastly improving accessibility for VoiceOver.
• 📸 Before/After: Not applicable (invisible hit-target and VoiceOver changes).
• ♿ Accessibility: Combined children for VoiceOver to read the row naturally as a single element and added the .isSelected trait to announce state correctly.

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PR created automatically by Jules for task 11900948141985423801 started by @acebytes

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