🎨 Palette: 탭 컴포넌트 키보드 탐색(Roving tabindex) 지원

[seonghobae]

💡 What: KRDS 탭 컴포넌트에 Roving tabindex와 방향키 탐색 기능을 추가했습니다.
🎯 Why: 기존에는 모든 탭이 자연스러운 탭 순서(natural tab order)에 포함되어 있어 키보드 사용자가 탭 패널 내용으로 진입하기 위해 모든 탭을 순차적으로 통과해야 하는 불편함이 있었습니다.
📸 Before/After: 시각적 변화는 없지만, 키보드 탐색 경험이 크게 개선되었습니다. 방향키로 탭 전환이 가능합니다.
♿ Accessibility: WAI-ARIA 탭 권장 패턴(Roving tabindex)을 준수하도록 개선하고, tablist에 aria-label을 추가해 컨텍스트를 명확히 했습니다.

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PR created automatically by Jules for task 2449457969914145042 started by @seonghobae

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