🎨 Palette: Add explicit instructional text for game controls

[EiJackGH]

💡 What: Added visible, non-blocking instructional text indicating that "Space" or "Up Arrow" can be used to jump in the Mario game.
🎯 Why: When building interactive HTML5 widgets or games with custom keyboard event bindings, users lack visual cues about the required inputs. Adding explicit instructions reduces cognitive load and prevents users from guessing how to interact with the game.
📸 Before/After: Added a new div#instructions to the UI with pointer-events: none styling.
♿ Accessibility: Ensures that users immediately know how to interact with the game without needing to guess the custom keyboard bindings. The instructions are placed as a sibling to the dynamic score content, preventing screen readers from repeating the static text if placed in a live region.

---

PR created automatically by Jules for task 12622179706617106021 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.