🎨 Palette: Improve keyboard accessibility and focus states

[n24q02m]

💡 What: Added tabindex="0", role="region", and aria-label to the table's .scroller container. Added clear, distinct :focus-visible outlines to all major interactive elements.
🎯 Why: Without these changes, keyboard-only users could not scroll the data table horizontally if it overflowed on smaller screens, and the default focus indicators were too subtle or missing on interactive buttons/links.
📸 Before/After: Focus states now display a solid 2px accent outline with an offset, improving visibility over standard browser defaults.
♿ Accessibility: Addresses WCAG Success Criteria 2.1.1 (Keyboard) and 2.4.7 (Focus Visible) by making overflow regions keyboard-navigable and ensuring clear visual focus rings.

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PR created automatically by Jules for task 16294318137641775467 started by @n24q02m

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