Regarding UX.
I like the idea of getting the kb directly displayed in a modal and it's a good starting point.
But the view of the content of an article is bad currently.
We move to a full layout of GLPI if we click on an article's title, and we don't have anymore a "use as solution" button.

Also, this part is very badly displayed:

I think we should probably remove it completely in the modal

There are a few things that aren't handled yet like linking the KB article in addition to just copying the content, pagination, etc.

This work is going to need be more complex so I put it to draft.

It is rough, but here is a replacement UI proposal for searching solutions:

I pushed commits that add this and it should be functional. The only main thing missing is pagination.

When you click the button to search for a solution, it presents you with a list of matching articles rather than the table that was there previously. Each result has two buttons; A button to use it as the solution and a button to preview the article. If you preview an article, the results are hidden and the "full" form of the article is shown in its place in the modal. A button at the top of the preview lets you go back to the results. Searching from inside this modal refreshes the results via AJAX.

It should be good like this.