test(12.2-05): prove relation child and protected file scoping through the router

- acme.deferred fixture plugin over testdata/deferred (test-only), two
  controllers, recording Form and Relation hooks, two admins
- TestRelationChildScope*: every child route answers 404 for another
  parent, a hidden parent and another admin's pending child, changes
  nothing; undeclared toolbar buttons 403 before SQL; pivot whitelist
- TestProtectedFile*: foreign, pending and public files 404; only jpeg,
  png, gif and webp inline; nosniff, no-store and sandbox CSP everywhere

modules/cabana/testdata/deferred/models/gadget/columns.yaml

@@ -0,0 +1,10 @@
+columns:
+    name:
+        label: Name
+        searchable: true
+    released_on:
+        label: Released on
+        type: date
+    opens_at:
+        label: Opens at
+        type: time