feat(build): scaffold working admin controllers with model, AdminFS and delete (quick-261028-pq8)

- make:admin-controller edits the singular of its name (--model overrides):
  ModelName, modelClass and the YAML under models/<model>/
- NewRecord returns &models.<Model>{} when the model exists; otherwise the
  nil body stays and the command says to run make:model
- config_list.yaml offers create and delete with showCheckboxes
- registry.gen.go embeds controllers/*/*.yaml and models/*/*.yaml once they
  exist and exposes generatedAdminFS(); scaffolded plugins implement
  pact.AdminAssets through it, and a plugin without AdminFS gets a note
- blog example moves its YAML to models/post; docs and help text follow

docs/plugins/registration.md

@@ -108,7 +108,7 @@ plugins/acme/blog/
 ├── go.mod              the plugin module, requiring the framework
 ├── plugin.go           the Plugin type, its capabilities and init registration
 ├── routes.go           the Routes method
-├── registry.gen.go     generated lists of models, migrations, commands, jobs and admin controllers
+├── registry.gen.go     generated lists of models, migrations, commands, jobs and admin controllers, and the embedded admin YAML
 ├── classes/            services and hooks
 ├── config/config.yaml  default configuration
 ├── console/            console commands