⚡ Bolt: Optimize scroll-to-top button listener

[kaitoartz]

💡 What: Cached visibility state and added { passive: true } to the scroll listener for the scroll-to-top button.
🎯 Why: Avoids continuous DOM classList manipulation on every scroll event and allows the browser to optimize scrolling without waiting for preventDefault().
📊 Impact: Reduces layout thrashing and main thread blocking during scrolling, freeing up CPU cycles.
🔬 Measurement: Verify scroll-to-top button toggles correctly at 300px threshold with lower CPU usage profiling during rapid scrolls.

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PR created automatically by Jules for task 3965983148770198588 started by @kaitoartz

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