feat(18.1-01): task 3 flat reorder on the server

- config_reorder.yaml without parentColumn on a record with no parent_id
  column compiles as a flat (WinterCMS Sortable) reorder; maxDepth above 0
  on it fails boot, an explicit parentColumn still means a tree
- ListReorder.Flat and AdminReorderTree.Flat (flat, omitempty); flat nodes
  carry parent_id null, a save writes only the sort column, a parent is a
  422 on nodes (reorder.flat_parent); 409 and duplicate rules unchanged
- swag descriptions, OpenAPI and schema.d.ts regenerated
- acme.catalog badges reorder fixture, TestReorderFlatCompile and
  TestReorderFlatSmoke; docs Flat reorder section and cabana README

modules/cabana/testdata/catalog/controllers/badges/config_list.yaml

@@ -4,4 +4,4 @@ title: Badges
 recordUrl: acme/catalog/badges/update/:id
 recordsPerPage: 20
 toolbar:
-    buttons: [create]
+    buttons: [create, reorder]

modules/cabana/testdata/catalog/controllers/badges/config_reorder.yaml

@@ -0,0 +1,3 @@
+title: Reorder badges
+nameFrom: name
+modelClass: Badge