🎨 Palette: Highlight keyboard shortcuts with <kbd> tags

[EiJackGH]

💡 What: Added semantic <kbd> tags to the game instructions for "Space" and "↑", along with physical key styling and improved contrast via text shadows.
🎯 Why: Explicitly highlighting keyboard controls improves intuitiveness and discoverability for users, making it immediately obvious which keys to press.
📸 Before/After: The instructions changed from plain text to explicit, visually distinct physical keys.
♿ Accessibility: Semantic HTML was used for the keys. A text-shadow was added to the container to ensure high contrast against the bright blue background, while the shadow was neutralized on the <kbd> elements themselves to ensure they read cleanly against their own gray backgrounds.

Note on custom CSS: Added custom styling for kbd directly to the internal style block as there are no existing utility classes for kbd in the project.

---

PR created automatically by Jules for task 6083933013383335673 started by @EiJackGH

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.