タブ・インジケータ滑走

Implement the following web visual TECHNIQUE as a small, self-contained demo (single HTML file, inline CSS/JS; GSAP via CDN is allowed if it fits the recipe). Invent your own placeholder content (original text/shapes/colors) — do NOT copy any existing site's content or branding.

## Technique: Sliding Tab Indicator (タブ・インジケータ滑走)

What happens: タブ切替時、下線や背景ピルが選択位置へぬるっと滑走移動する

## Implementation recipe (normative)

JSでoffsetLeft/widthを測り共有バーをtranslate。View Transitions APIなら自動モーフ(→A-6)

## Timing values chosen by the user (normative — use these exact values)

- Easing: `cubic-bezier(0.22, 1, 0.36, 1)`
- Base duration: 2.60s
- Intensity 1/5: Keep amplitudes minimal (2-8px movements, opacity-led, no overshoot) — the motion should be barely-there and elegant.

## Quality bar

- Runs at 60fps; animate only transform/opacity/filter where possible.
- Make the initial state legible immediately. Preserve the full timing above, including deliberately slow transitions. Repeat only when the recipe calls for a loop; give finite effects a clear ending and replay action.
- Respect prefers-reduced-motion: show a legible resting state without autoplay. Keep every operation available through keyboard and touch; allow deliberate playback of the effect for inspection.
- Difficulty reference: 中. If the recipe mentions specific libraries or shader work, follow it rather than substituting a simpler approach.