Co-op matches of editor campaigns

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lang/en.lang

@@ -659,6 +659,10 @@ net.no_rooms = No open matches.
 net.create = Create match
 net.coop_mission = Co-op campaign: mission {0} ({1})
 net.coop_create = Co-op campaign
+net.coop_editor = Editor campaign
+net.coop_builtin = Built-in campaign
+net.coop_editor_mission = Editor campaign {0}: mission {1} ({2})
+net.coop_editor_none = No mission of the editor campaign fits co-op (map at least 72x72, a goal besides rival masters)
 net.join = Join
 net.join_hint = Match code
 net.seats = Seats