runners/recentdocuments: match only local file names

1. Restrict the KActivitiesStats URL query to local file paths (URL starting with /). This fixes a regression introduced with !2273 (merged) where the query would also return recently used web URLs that will then be used with a nonsensical file name and empty title. (Or do we actually want to include these web locations and handle them better by putting the URL as the title? Running them does work, it just looks broken as of now.)
2. Exclude matches where the search term does not occur in the file name, so that searching "a" only matches "a.txt", but not "a/b.txt". Imo it doesn't make a lot of sense to recursively list all recently used files of a directory that matches a query. An alternative would be to then instead return the matching parent directory, i.e. "a". Or at least weight such results lower.