feat(17-01): tree reorder page and singleton admin controllers

- cabana: config_reorder.yaml (title, nameFrom, modelClass, parentColumn,
  sortColumn, maxDepth, partition) with fail-loud boot checks and the
  built-in reorder toolbar button; list schema carries reorder
- GET/POST {controller}/reorder: scoped set (ListExtendQuery plus the
  partition) locked FOR UPDATE, 409 reorder_stale on any set difference,
  422 for duplicates, foreign parents, cycles and maxDepth, both columns
  written without model hooks
- pact.AdminSingleton: GET {controller}/singleton (first or create, form
  scope checked), form schema singleton, list/create/bulk/delete 404,
  no config_list.yaml needed
- swag, inventories, token classes, CSRF walk, conformance cases, backend
  lang reorder.stale and load_failed, reorder and singleton smoke tests, docs

modules/cabana/testdata/companions/controllers/links/config_list.yaml

@@ -4,4 +4,4 @@ title: Links
 recordUrl: acme/companions/links/update/:id
 recordsPerPage: 20
 toolbar:
-    buttons: [create]
+    buttons: [create, reorder]

modules/cabana/testdata/companions/controllers/links/config_reorder.yaml

@@ -0,0 +1,10 @@
+title: Reorder links
+nameFrom: title
+modelClass: Link
+parentColumn: parent_id
+sortColumn: sort_order
+maxDepth: 3
+partition:
+    column: group_id
+    relation: group
+    label: Group

modules/cabana/testdata/companions/controllers/profiles/config_form.yaml

@@ -0,0 +1,4 @@
+name: Site profile
+form: ~/plugins/acme/companions/models/profile/fields.yaml
+modelClass: Profile
+defaultRedirect: acme/companions/profiles

modules/cabana/testdata/companions/models/link/fields.yaml

@@ -3,6 +3,11 @@ fields:
         label: Title
         type: text
         required: true
+    group:
+        label: Group
+        type: relation
+        nameFrom: title
+        emptyOption: backend::lang.form.none
     type:
         label: Type
         type: dropdown

modules/cabana/testdata/companions/models/profile/fields.yaml

@@ -0,0 +1,4 @@
+fields:
+    title:
+        label: Title
+        type: text