⚡ Bolt: Eliminate O(N) DOM queries inside requestAnimationFrame loop

[kaitoartz]

💡 What: Caches the .intro-card DOM element reference during the HyperScrollIntro initialization and tracks its active state (isCardActive) to conditionally update its class only when the state changes.

🎯 Why: Inside the 60fps requestAnimationFrame loop (HyperScrollIntro.startLoop()), calling querySelector('.intro-card') and indiscriminately calling classList.toggle() for potentially hundreds of items causes O(N) DOM read/write operations per frame. This is a severe anti-pattern that leads to unnecessary CPU overhead, GC pressure, and layout thrashing, especially on low-end and mobile devices.

📊 Impact: Reduces DOM read/write operations for .intro-card elements from O(N) per frame (N = number of intro items) to 0 operations per frame, strictly executing a single write ONLY when an item enters or exits the focus range. CPU usage during the intro sequence should be measurably lower.

🔬 Measurement: Use Chrome DevTools Performance tab to profile the intro scroll sequence before and after this change. Observe the reduction in the amount of time spent in "Scripting" and "Rendering" phases, specifically the elimination of repeated querySelector calls in the flame chart.

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PR created automatically by Jules for task 8938071672307508152 started by @kaitoartz

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