Change history modal now opens reliably with the right data

The change history modal had a few coupled issues that made it feel unreliable.

• It was trying to fetch data on component mount instead of when you actually opened the modal — so the very first article you viewed often had a brief flash of "loading…".
• The API call wasn't filtering by article ID correctly, so the modal could occasionally display history entries from a different article.
• The infinite-scroll pagination wasn't carrying the article filter through to subsequent pages.

All three got rewired in this release. The modal now fetches on open, scopes correctly to the article you're viewing, and paginates without losing the filter. A small loading flag makes the initial state feel intentional instead of flickery.