Co-op campaign "League against the Lightwatch": 20 missions, selectable on the Match page

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

lang/en.lang

@@ -661,6 +661,7 @@ 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_league = League against the Lightwatch
 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