🎨 Palette: Add explicit focus styles for keyboard accessibility

[n24q02m]

💡 What: Added an explicit :focus-visible outline to all interactive elements globally via CSS.
🎯 Why: Browser default focus indicators are often insufficient or invisible, making keyboard navigation difficult.
📸 Before/After: (Verified visually via Playwright during development)
♿ Accessibility: Improves WCAG compliance for focus indicators, ensuring keyboard users can clearly see which element has focus.

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PR created automatically by Jules for task 12354228393554895441 started by @n24q02m

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