E2E: Refactor GridRowScrollPinning to Hybrid rAF Engine

This ticket documents the pivot to the Hybrid Engine for the GridRowScrollPinning addon.

The initial implementation relied on intercepting VDOM deltas directly as they arrived from the App Worker. However, testing revealed that native browser scrolling runs at 60fps, while worker updates are much slower (often >50ms during heavy layout). This discrepancy meant that the addon was only updating the pinning transform when a message arrived, rather than staying perfectly synced with the physical scrollbar thumb, causing extreme visual jitter.

The Pivot: We have refactored the addon into a Hybrid architecture:

1. Stateful Updates: VDOM updates from the App Worker (onDeltaUpdate) no longer mutate the DOM. They only update an internal workerScrollTop reference state.
2. Scroll Driven: A native scroll event listener is attached to the Grid Wrapper node.
3. rAF Loop: The native scroll event triggers a requestAnimationFrame loop.
4. Continuous Pinning: Inside the rAF loop, the addon calculates deltaY (actualScrollTop - workerScrollTop) and applies the translate3d CSS transform to the Grid Body content node on every frame, achieving perfect 60fps optical pinning regardless of worker latency.
5. Hysteresis Logic: The addon enters an isPinned state when deltaY > rowHeight and stays pinned until deltaY falls below 2px to prevent flickering on micro-scrolls.

Completed Changes:

• Completely rewrote src/main/addon/GridRowScrollPinning.mjs to implement the requestAnimationFrame and native scroll listener loop.
• Reverted the registration lifecycle in src/grid/ScrollManager.mjs to properly use afterSetMounted, as the addon now requires the DOM to be ready to attach the scroll listener.
• Temporarily added console logging logic for debugging.

This sub-ticket serves to commit this architectural baseline to the repository before further exploration of sync frequency vs performance.