🎨 Palette: Add <kbd> styles for keyboard instructions

[EiJackGH]

💡 What: Wrapped the 'Space' and '↑' text in the game instructions with semantic <kbd> tags and added styling to make them look like physical keys.
🎯 Why: To make the custom keyboard controls more intuitive and explicitly clear to users by distinguishing them visually from regular text.
📸 Before/After: The instruction previously read as plain text: "Press Space or ↑ to jump!". It now shows stylized keycap buttons for the inputs.
♿ Accessibility: Improved semantic meaning for screen readers and assistive tech by explicitly denoting keyboard input using the native HTML <kbd> tag. Added the styles to the existing internal <style> block to match the project's current styling approach without adding heavy new UI dependencies.

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PR created automatically by Jules for task 15971047846561862910 started by @EiJackGH

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