🎨 Palette: Add instructional text to mario game

[EiJackGH]

💡 What: Added instructional text indicating the required keybindings ("Press Space or Up Arrow to jump") to the Mario game widget.
🎯 Why: Users often do not know the required keyboard inputs for interactive web canvas games. Providing explicit instructions reduces friction and improves the initial user experience.
📸 Before/After: Verified visually via local playwright script (screenshot).
♿ Accessibility: The instructional text is rendered outside of any live regions to avoid repetitive screen reader announcements, and utilizes pointer-events: none to avoid interfering with pointing device interactions.

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PR created automatically by Jules for task 10805179838916068662 started by @EiJackGH

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