🎨 Palette: Enhance Mario Game UX and Accessibility

[EiJackGH]

💡 What: Added explicit keyboard instructions, separated static "Score:" label from dynamic value, and added aria-live to the score value. Also added pointer-events: none to instructions overlay.
🎯 Why: Users didn't know how to jump unless they looked at the source code. Screen readers would awkwardly read "Score: 1... Score: 2..." repeatedly. Now the score just announces the number politely, and the instructions are visible without blocking clicks.
♿ Accessibility: Separated static labels from dynamic values and applied aria-live="polite" and aria-atomic="true" to the dynamic score value.
📸 Tested via Playwright UI screenshot verification.

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PR created automatically by Jules for task 3465017335443844792 started by @EiJackGH

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