🎨 Palette: Add explicit keyboard instructions to Mario game

[EiJackGH]

💡 What: Added explicit keyboard instructions ("Press Space or ↑ to jump") below the score in the Mario game canvas.
🎯 Why: Without visual cues, users have to guess the custom keyboard controls to play the game, leading to a poor initial user experience.
📸 Before/After: See screenshot provided during UI verification.
♿ Accessibility: Ensures the instruction text is available to screen readers while keeping it visually distinct via CSS. Added pointer-events: none to avoid blocking interactions.

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PR created automatically by Jules for task 4041746752226331474 started by @EiJackGH

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