🎨 Palette: Add keyboard instructions and accessibility to Mario game

[EiJackGH]

💡 What

Added visible keyboard instructions ("Press Space or Up Arrow to jump") to the Mario game overlay and made the dynamic score counter screen-reader accessible.

🎯 Why

New users often don't know the controls for embedded mini-games, leading to frustration. By making the controls visible, the interaction becomes immediately intuitive.

♿ Accessibility

Added aria-live="polite" and aria-atomic="true" to the #score element so screen readers gracefully announce the score updates as the game progresses. The static instructions were purposefully kept outside the live region to prevent redundant announcements on every score tick.

📸 Before/After

(Verified locally using Playwright screenshots)

• Before: Only the score was visible. Screen readers did not announce score updates.
• After: Clear keyboard instructions appear below the score. Screen readers announce score changes naturally.

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PR created automatically by Jules for task 6090730753538354458 started by @EiJackGH

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