🎨 Palette: Add ARIA labels to admin icon buttons

[ralksta]

💡 What: Added aria-label attributes to icon-only buttons across the admin panel, and wrapped text-based icons (like "✕") in aria-hidden spans.\n🎯 Why: Ensures screen readers can correctly announce the purpose of these interactive elements.\n📸 Before/After: Visuals remain unchanged; structural accessibility improved.\n♿ Accessibility: Substantially improves navigation for assistive technologies.

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PR created automatically by Jules for task 13866304941231616183 started by @ralksta

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