🎨 Palette: [UX improvement] Add global focus-visible styles

[mapleleaflatte03]

💡 What: Added global :focus-visible outline styles for interactive elements in meridian.css.
🎯 Why: Improve keyboard navigation accessibility by providing a clear visual indicator of the currently focused element, crucial for keyboard users.
📸 Before/After: Screenshots and video recordings have been verified using Playwright to show the focus outline applying to buttons and form inputs on the Trust Ops page.
♿ Accessibility: Addresses a critical a11y requirement (WCAG 2.4.7 Focus Visible) without adding unnecessary visual noise for standard mouse users.

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PR created automatically by Jules for task 3969092485688405954 started by @mapleleaflatte03

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