fix(web): keep the last diff file reachable with word wrap

[enisze]

What Changed

Adjust diff panel virtualization in word-wrap mode to render bounded chunks around the viewport, allowing wrapped rows to be measured accurately and keeping the final file's content reachable. Scroll mode retains its existing minimal chunk size.

Why

Long wrapped lines can occupy multiple visual rows, but estimating each off-screen line at a single row underestimates the total scroll height. This caused the scrollbar to reach the bottom before the tail of the last diff file was accessible. Measuring larger chunks lets the virtualizer extend the scroll range correctly.

UI Changes

This fixes scrolling behavior in the web diff panel when word wrap is enabled. No screenshots or video included because the change corrects an existing scrolling bug without introducing a new visual design or animation.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes