🎨 Palette: Add keyboard instructions and accessible score to Mario Game

[EiJackGH]

💡 What:
Added explicit on-screen text telling the user to "Press Space or Up Arrow to jump" and made the score updates accessible. Removed invalid venv entry from requirements.txt to fix dependencies issue.

🎯 Why:
Previously, the game controls were hidden unless the user guessed or read the source code. The dynamic score was also completely invisible to screen readers, meaning visually impaired users had no way of knowing their score was updating.

📸 Before/After:
(See verification screenshots - instructions text now appears clearly under the score).

♿ Accessibility:

• Added aria-live="polite" and aria-atomic="true" to the #score element so screen readers can announce dynamic score updates.
• Ensured the instruction text is accessible and clearly styled with high contrast text against the blue background.

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PR created automatically by Jules for task 11275990256214276973 started by @EiJackGH

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