Changed files: whole line counts, one file's diff on a click

When an agent works in a folder without git, its card lists the files it changed. The lines added and removed now stand in columns of their own and no longer break onto the next line when a file name is long. A click on a text file opens the diff of that file alone, with a link to the whole diff beside it, so reading one file's changes no longer means scrolling through all of them.