🎨 Palette: Add keyboard instructions and ARIA updates to Mario game

[EiJackGH]

💡 What

Added visible instructions explaining the keyboard controls ("Press Space or Up Arrow to jump") to the Mario game overlay.

🎯 Why

Previously, the game relied entirely on users guessing the controls or checking the source code. This small text addition eliminates friction and makes the interaction immediately intuitive for new users.

📸 Before/After

• Before: Only "Score: 0" was visible.
• After: "Score: 0" and "Press Space or Up Arrow to jump" are both visible in the top left.

♿ Accessibility

• Added aria-live="polite" and aria-atomic="true" to the #score element so screen readers will announce score updates correctly as the user progresses.
• Ensured static instructional text was kept completely separate from the aria-live region to prevent screen readers from annoyingly repeating the static instructions every time the score changes.

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PR created automatically by Jules for task 18112295107133983020 started by @EiJackGH

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