🎨 Palette: Make scrollable data table keyboard accessible

[n24q02m]

💡 What: Added keyboard accessibility to the overflow data table by adding tabindex="0", role="region", aria-label, and a clear :focus-visible state.
🎯 Why: Scrollable containers that clip overflow content are inaccessible to keyboard-only users unless they are explicitly placed in the tab order. Without this, keyboard users cannot scroll the table horizontally to see all data.
📸 Before/After: Visual focus state is now evident around the table when tabbed to.
♿ Accessibility: Ensures compliance with WCAG 2.1 SC 2.1.1 (Keyboard) for scrollable regions.

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PR created automatically by Jules for task 348049537329966819 started by @n24q02m

[google-labs-jules]

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