⚡ Bolt: Optimize scroll event listener layout thrashing

[kaitoartz]

💡 What: Throttled scroll event listeners using requestAnimationFrame and state caching for the "Scroll to Top" and navigation link states.
🎯 Why: Scroll events fire at a very high rate. Continually calling classList.add or remove on every scroll tick causes unnecessary style recalculations and layout thrashing, even if the class state isn't actually changing.
📊 Impact: Prevents main-thread blocking and wasted CPU cycles during scrolling, resulting in a noticeably smoother scrolling experience without jank.
🔬 Measurement: Use Chrome DevTools Performance profile while scrolling. The number of 'Recalculate Style' events triggered during scroll is significantly reduced.

---

PR created automatically by Jules for task 18251787597286397830 started by @kaitoartz

[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.