🎨 Palette: [UX improvement] Add keyboard instructions and score accessibility

[EiJackGH]

💡 What

Added a visible instruction box in the top right corner of the Mario game interface and improved the accessibility of the live score updates.

🎯 Why

• Instructional feedback: The Mario game previously lacked any explicit indication of how to jump (Space or Up Arrow). This caused a potential friction point for users unaware of typical keyboard gaming conventions.
• Accessibility: Live updating elements like a score count should be announced politely to screen readers, allowing visually impaired users to track their progress.

♿ Accessibility

• Added aria-live="polite" and aria-atomic="true" to the #score element to announce point increments safely.
• Did not hide text hints to screen readers, as instructions are vital for general interactive accessibility.

📸 Before/After

(Verified visually with Playwright snapshot: the instructions perfectly sit cleanly with a semi-transparent dark background without obstructing gameplay elements.)

Other Details

• Fixed requirements.txt which mistakenly included venv, breaking local standard setups.

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PR created automatically by Jules for task 15769575207908622098 started by @EiJackGH

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