🧪 Add tests for curriculum pagination system

[dynamikdev]

🎯 What: Added tests for the missing curriculum_page_button_system to fulfill the task request.
📊 Coverage: Covered edge cases (hidden UI, empty pages array), boundaries (decrementing at 0, incrementing at max), and happy paths for both "Prev" and "Next" buttons modifying the CurriculumState.
✨ Result: Increased testing coverage and confidence that pagination limits operate correctly and prevent underflow/overflow panic scenarios.

---

PR created automatically by Jules for task 18335842861004033861 started by @dynamikdev

[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.