🎨 Palette: Add keyboard instructions to Mario Game

[EiJackGH]

💡 What: Added explicit on-screen keyboard instructions ("Press Space or ↑ to jump!") to the Mario Game UI.
🎯 Why: Without visual cues, users may not know the required keybindings to play the game, leading to frustration.
📸 Before/After: The game previously only displayed the score. It now displays instructions directly below the score.
♿ Accessibility: Instructions are visible and accessible to screen readers. The element uses pointer-events: none to ensure it does not block any interaction with the game canvas.

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PR created automatically by Jules for task 15395852756696330994 started by @EiJackGH

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