🎨 Palette: Add physical styling to keyboard instructions

[EiJackGH]

💡 What: Added <kbd> tags around the "Space" and "↑" instructions in the Mario game view and applied CSS to give them a physical key appearance. Logged the learning in the palette journal.
🎯 Why: To improve the intuitiveness and discoverability of custom keyboard controls against a dynamic background, reducing cognitive load for users trying to figure out how to interact with the game.
📸 Before/After: The instructions changed from plain text to visually distinct keyboard keys.
♿ Accessibility: Wrapping keyboard shortcuts in <kbd> tags improves semantic HTML structure, and the high-contrast physical styling ensures they are readable.

Note: Custom CSS was added to the internal <style> block of the .njk file because this file does not use utility classes (like Tailwind) and relies entirely on internal vanilla CSS for its styling. This was the only way to adhere to the existing pattern while achieving the necessary styling.

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PR created automatically by Jules for task 11160904287311225231 started by @EiJackGH

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